Abeykoon, Jithma P.

Introduction Minimal residual disease (MRD) status at day 100 following autologous stem-cell transplant (ASCT) in multiple myeloma (MM) patients is an important determinant of prognosis. Bone marrow (BM) based assays, i.e. next-generation flow cytometry (NGF) or next-generation sequencing (NGS) that are currently used in determining MRD are vulnerable to sampling biases due to patchy marrow involvement and extramedullary disease. BM examination alone may lead to false-negative results. MRD assessment through newer, more sensitive peripheral blood based methodologies such as mass spectrometry (MS) can potentially overcome the limitations associated with BM based assays. At our institution, traditional immunofixation electrophoresis (IFE) has been replaced by a MS method termed Mass-Fix which utilizes the unique light chain mass associated with each patient's monoclonal protein to monitor disease over time. In this study, we assessed the prognostic impact of serum Mass-Fix MRD status in MM patients who were MRD negative by NGF around day 100 post-ASCT. Methods Patients with MM who underwent ASCT between 01/01/2015 and 12/31/2018 at Mayo Clinic, Rochester were included in this study provided they had attained post ASCT day 100 complete response (CR) by IMWG 2016 criteria and MRD- state as assessed by BM based NGF, utilizing 2 eight-color tubes (total 10 colors), with a minimum sensitivity 10-5. Presence of non-secretory MM and unavailability of pre-ASCT serum samples or serum IFE results were important exclusion criteria. Peripheral blood samples drawn concurrently with the BM assessment were evaluated by Mass-Fix as described previously (Mills et al., Clin. Chem, 2016). The isotype and mass of the M-protein light chain (LC) obtained by Mass-Fix were compared to the pre-ASCT M-protein LC and/or IFE isotype. Patients with the following genetic alterations: deletion 17p, translocation (4;14), (14;16), t(14;20) and1q gain/amplification and were considered high risk. All time-to event analyses were performed on JMP 14.1.0 from the time of ASCT using the Kaplan-Meier method. Results Sixty-two patients with MM (57 newly diagnosed and 5 relapsed/refractory) who underwent ASCT and were MRD- by BM based NGF around day 100 (range: day 60-120) were included in the study. Median age at ASCT was 61 (range: 40-76) years and 61% were males. Thirty (48%) patients had IgG MM, 15 (25%) patients had IgA MM and 17 (27%) patients had light chain only disease. Forty-one (66%) patients received bortezomib, lenalidomide and dexamethasone (VRD) as induction regimen. Median time from diagnosis to ASCT was 6 months (IQ range: 4.7-7.2). Pre-ASCT fluorescence in- situ hybridization data were available on 47 (76%) patients; 23 (49%) were high risk. Of 62 patients, all of whom were day 100 MRD- by NGF, 36 (58%) patients had Mass-Fix identified MRD (MRD+). MRD positivity by Mass-Fix around day 100 was observed in 70% of patients with high risk MM versus 71% of patients with standard risk MM, p=0.9. The median follow-up was 18 months (95%CI: 14-21); 19 months (95%CI: 15-21) for patients who were MRD+ by Mass-Fix versus 17 months (95%CI: 12-21) for those who were MRD- by Mass-Fix at day ~100, p=0.5. Of 57 (92%) patients who received post ASCT maintenance therapy, 32 (89%) were MRD+ and 25 (96%) were MRD- by Mass-Fix, p=0.5. Eighty-seven percent of patients with IgG MM had MRD+ status by Mass-Fix at day~100. By contrast, only 33% and 30% of patients with IgA MM and light chain MM, respectively, had MRD+ status at day 100; p<0.0001. This suggests that IgG half-life which is longer than that of IgA or free light chains may affect the day 100 MRD status. At 18 months, 76% and 93% of patients, who were MRD+ and MRD- , respectively by Mass-Fix were alive and free from disease progression, p=0.03 (Table 1, Figure 1a). At 18 months after ASCT, none of the patients who were MRD- by Mass-Fix required salvage treatment following ASCT while 25% of patients who were MRD+ by Mass-Fix required next line of therapy due to disease progression, p=0.05 (Table 1, Figure1b). Conclusion Our data suggest that outcomes [progression free survival (PFS) and time-to-next therapy (TTNT)] of patients with MM who are in CR, and have achieved MRD- state by BM NGF post ASCT, can be adversely impacted if there is concurrent evidence of serum monoclonal protein by Mass-Fix, thereby demonstrating incremental prognostic value of this sensitive assay in clinical practice. Disclosures Murray: The Binding Site: Patents & Royalties: US Patent Rights on Mass Spectroscopy Licensing agreement with The Binding Site, Research Funding. Dispenzieri:Akcea: Consultancy; Intellia: Consultancy; Janssen: Consultancy; Pfizer: Research Funding; Takeda: Research Funding; Celgene: Research Funding; Alnylam: Research Funding. Dasari:The Binding Site: Patents & Royalties: US Patent Rights on Mass Spectroscopy Licensing agreement with The Binding Site, Research Funding. Gertz:Teva: Speakers Bureau; Alnylam: Consultancy; Prothena Biosciences Inc: Consultancy; Janssen: Consultancy; Spectrum: Consultancy, Research Funding; Annexon: Consultancy; Appellis: Consultancy; Johnson and Johnson: Speakers Bureau; DAVA oncology: Speakers Bureau; Celgene: Consultancy; Research to Practice: Consultancy; Abbvie: Other: personal fees for Data Safety Monitoring board; Physicians Education Resource: Consultancy; Medscape: Consultancy, Speakers Bureau; Springer Publishing: Patents & Royalties; Amyloidosis Foundation: Research Funding; International Waldenstrom Foundation: Research Funding; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy; Ionis/Akcea: Consultancy; Proclara: Membership on an entity's Board of Directors or advisory committees; i3Health: Other: Development of educational programs and materials. Dingli:Karyopharm: Research Funding; Millenium: Consultancy; Rigel: Consultancy; Janssen: Consultancy; alexion: Consultancy. Lacy:Celgene: Research Funding. Leung:Omeros: Research Funding; Aduro: Membership on an entity's Board of Directors or advisory committees; Prothena: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding. Kumar:Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Takeda: Research Funding. Kapoor:Takeda: Honoraria, Research Funding; Janssen: Research Funding; Celgene: Honoraria; Sanofi: Consultancy, Research Funding; Amgen: Research Funding; Glaxo Smith Kline: Research Funding; Cellectar: Consultancy.

Introduction Langerhans cell histiocytosis (LCH) is an uncommon histiocytic disorder which is now categorized as a hematopoietic neoplasm. Most treatment and outcomes data in LCH are derived from pediatric studies, and there is a lack of FDA-approved treatment options for adult LCH. There is some evidence that cladribine may be toxic to monocytes and monocyte-derived dendritic cells. In this study, we report the efficacy of cladribine in adult LCH patients seen at our institution. Methods We retrospectively reviewed the charts of all LCH patients seen at our institution between 1998 and 2018. Where necessary, the radiological images and histopathological slides were reviewed by an expert radiologist and pathologist. Since prospective uniform response assessment was not performed, we utilized the clinical documentation and radiological reports to assess the overall response rate (ORR). All time to event analyses were performed from the time of cladribine initiation. Results We included a total of 37 adult LCH patients in the study. The median age at diagnosis for this cohort was 35 years (range, 21-76), and 51% were males. Although 31 (84%) patients had multi-system disease, all patients had more than one LCH lesion (multifocal). Most commonly involved organs were bone (65%), lung (60%), skin (38%), lymph nodes (30%), and pituitary/hypothalamus (27%). BRAF-mutational analysis was performed in 13 patients, with 7 (54%) demonstrating the presence of BRAF-V600E mutation. Cladribine was administered as first line therapy in 22 (59%) patients and subsequent line treatment in 15 (41%). Of the 15 patients who received cladribine in subsequent line, surgery (n=3), radiation (n=3), steroids (n=3), antibiotic with inhaled steroids (n=1), vinblastine (n=3), topical nitrogen mustard cream (n=1) and vemurafenib (n=1) were the treatments utilized before the initiation of cladribine. Two patients received the drug more than once during the course of their disease. The dosing of cladribine for all patients was based on one of the two intravenous regimens (0.14 mg/kg for days 1-5 every 28 days or 5 mg/m2 for days 1-5 every 28 days). The median follow-up for the entire cohort was 4.5 years (95% CI:2-7) and the treatment outcomes are shown in Table 1. Median number of cycles of cladribine administered was 1.5 (range, 1-9). Clinical/radiographic responses were noted in 29 (78%) patientsORR was 78%, with 24% complete responses and 54% partial responses (PR). Responses were seen in various disease sites: lung nodules/infiltrates (13/29, 45%), bone (12/29, 41%), lymph nodes (8/29, 28%), skin (3/29, 10%), pituitary/hypothalamus (4/29, 14%). Eight (22%) patients did not respond and had progressive disease (PD)- cystic/bullous lung disease (n=2), skin (n=2), abdominal/peritoneal lymph nodes (n=2), and hypothalamus (n=3).The treatment was well tolerated, with grade 3 or above adverse effects seen in three patients: two with lymphopenia requiring dose delays and one with congestive cardiac failure leading to drug discontinuation. After initial disease response, PD was seen in three patients. 89%, 78%, 64% of those who responded initially maintained their responses at years 1, 3, and 5, respectively (Table 1). The 5-year progression free survival (PFS) was 55% for the entire cohort. BRAF-status was evaluated on 13 of 37 patients in the entire cohort (35%): BRAFV600E positive [n=7 (53%)] and WT [n=6 (46%)]. Of the 7 patients who had BRAFV600E mutation, responses were seen in 71%, while 100% of those without BRAFV600E achieved a response (p=0.09). At the time of last follow-up, 9 patients (24%) were dead. Of those, cause of death were available on 5 patients; due to LCH (n=1), stroke (n=1), gastrointestinal hemorrhage (n=1), acute myeloid leukemia (n=2). Conclusion In our study, cladribine monotherapy yielded a high ORR, with the majority of patients achieving a PR. The responses were durable with a small risk of subsequent disease relapse. Responses were seen irrespective of the presence of BRAFV600E mutation. Cladribine was well tolerated overall, and may be considered a potential therapy for adult LCH patients. Disclosures Vassallo: Sun Pharmaceuticals: Research Funding; Pfizer: Research Funding; Bristol Myers Squibb: Research Funding; Sun Pharmaceuticals: Research Funding; Bristol Myers Squibb: Research Funding. OffLabel Disclosure: Cladribine for langerhans cell histiocytosis

Introduction: Waldenström macroglobulinemia (WM) is characterized by circulating monoclonal IgM and bone marrow infiltration with lymphoplasmacytic lymphoma (LPL) cells. Presently, there is limited data to guide prognosis or treatment options of WM based on the proportion of lymphocytes or plasma cells in the LPL population on the pathology. In this study, we aim to look at differing clinical features and outcomes of patients with WM based on the plasma cell (PC) percentage in the diagnostic bone marrow biopsy. Methods Patients with WM seen at Mayo Clinic, Rochester, MN between January 2001 and December 2017, with a bone marrow biopsy and a corresponding serum free light chain (FLC) examination at diagnosis of WM were included. The percentage of lymphocytes and PCs in the marrow biopsy was determined based on morphology ± immunohistochemistry. On immunohistochemistry, CD138 and/or MUM-1 positivity was used to quantify PCs, whereas CD20 and/or PAX5 were used to quantify lymphocytes. Patients with ≥10% PC component in the lymphoplasmacytic (LPL) cells on bone marrow biopsy were considered to have WM with excess plasma cells (WMEPC), while those with &lt;10% PCs were considered to have lymphocytic WM (LWM). Continuous variables were compared using Wilcoxon test and categorical variables were compared using Chi square test or Fisher's exact test. Time-to-next therapy (TTNT) was defined as the period from initiation of first line therapy to start of second line therapy or death due to any cause before second line therapy. Time-to-event analyses were conducted using Kaplan Meier method. Results: Of 228 evaluable patients, 147 (64%) had ≥ 10% PCs in the initial marrow biopsy. The median follow-up was 3.4 years (95% CI: 2.3-4.3 years) for LWM and 4.3 years (95% CI: 3.4-4.8 years) for WMEPC (p=0.33). The baseline characteristics of WMEPC versus LWM are depicted in Table 1. Patients with WMEPC had lower bone marrow involvement by LPL (30%) compared to LWM (60%; p&lt;0.001) at diagnosis, but the rate of symptomatic hyperviscosity was higher in WMEPC during the disease course (Table 1). The TTNT was shorter for WMEPC [2.6 years (95% CI: 1.8-4.5 years)] compared to LWM [4.5 years (95% CI 3.2-8.2)], although it did not reach statistical significance (p=0.09, Figure 1). There was a trend towards shorter OS for WMEPC [Not reached (95% CI 7.2- NR)] compared to LWM [10.7 years (95% CI 7.3 -12.1 years); p=0.28], Figure 2. Of the 228 patients, 79% (n=182) had data available for systemic therapy. The rate of PR or better with frontline therapy was higher in rates in LWM compared to WMEPC (61 % vs 42% p=0.02, Table 1). Among WMEPC cohort, patients receiving either a proteasome inhibitor (PI)-based or an immunomodulatory (IMiD)-based combination as frontline therapy (n=16) had higher rates of partial response or better (68%) compared to non-PI/non-IMiD based therapy (n=114), p=0.04. Conclusion: WM with excess plasma cells at diagnosis is associated with a trend towards shorter TTNT and OS compared to WM with &lt;10% plasma cells in the lymphoplasmacytic population at diagnosis. Our preliminary data shows higher rates of partial response or better with the use of PI/IMiD based therapy, but the small cohort size limits the strength of this finding which needs to be validated externally. Disclosures Ansell: Bristol-Myers Squibb: Research Funding; Trillium: Research Funding; Bristol-Myers Squibb: Research Funding; Bristol-Myers Squibb: Research Funding; LAM Therapeutics: Research Funding; Mayo Clinic Rochester: Employment; Regeneron: Research Funding; Trillium: Research Funding; Bristol-Myers Squibb: Research Funding; Affimed: Research Funding; Seattle Genetics: Research Funding; Regeneron: Research Funding; Bristol-Myers Squibb: Research Funding; Affimed: Research Funding; LAM Therapeutics: Research Funding; Trillium: Research Funding; Mayo Clinic Rochester: Employment; Seattle Genetics: Research Funding; Mayo Clinic Rochester: Employment; Bristol-Myers Squibb: Research Funding; Seattle Genetics: Research Funding; Mayo Clinic Rochester: Employment; Trillium: Research Funding; LAM Therapeutics: Research Funding; Affimed: Research Funding; Affimed: Research Funding; Bristol-Myers Squibb: Research Funding; Regeneron: Research Funding; Mayo Clinic Rochester: Employment; Trillium: Research Funding; Bristol-Myers Squibb: Research Funding; Seattle Genetics: Research Funding; Regeneron: Research Funding; LAM Therapeutics: Research Funding; LAM Therapeutics: Research Funding; Regeneron: Research Funding; Mayo Clinic Rochester: Employment; Affimed: Research Funding; Mayo Clinic Rochester: Employment; Trillium: Research Funding; Regeneron: Research Funding; Regeneron: Research Funding; Seattle Genetics: Research Funding; Affimed: Research Funding; Seattle Genetics: Research Funding; Mayo Clinic Rochester: Employment; Trillium: Research Funding; Trillium: Research Funding; Bristol-Myers Squibb: Research Funding; Trillium: Research Funding; LAM Therapeutics: Research Funding; LAM Therapeutics: Research Funding; Regeneron: Research Funding; Regeneron: Research Funding; Affimed: Research Funding; Seattle Genetics: Research Funding; LAM Therapeutics: Research Funding; Seattle Genetics: Research Funding; Seattle Genetics: Research Funding; Affimed: Research Funding; Mayo Clinic Rochester: Employment; LAM Therapeutics: Research Funding; Affimed: Research Funding. Gertz:Spectrum: Honoraria, Research Funding; Janssen: Honoraria; Celgene: Honoraria; Prothena: Honoraria; Alnylam: Honoraria; Ionis: Honoraria. Dingli:alexion: Consultancy; Janssen: Consultancy; Millenium: Consultancy; Rigel: Consultancy; Karyopharm: Research Funding. Nowakowski:Selvita: Membership on an entity's Board of Directors or advisory committees; NanoString: Research Funding; MorphoSys: Consultancy, Research Funding; Genentech, Inc.: Research Funding; F. Hoffmann-La Roche Ltd: Research Funding; Curis: Research Funding; Bayer: Consultancy, Research Funding; Celgene: Consultancy, Research Funding. Dispenzieri:Alnylam: Research Funding; Celgene: Research Funding; Takeda: Research Funding; Pfizer: Research Funding; Janssen: Consultancy; Intellia: Consultancy; Akcea: Consultancy. Lacy:Celgene: Research Funding. Kumar:Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Takeda: Research Funding. Kapoor:Janssen: Research Funding; Cellectar: Consultancy; Glaxo Smith Kline: Research Funding; Amgen: Research Funding; Takeda: Honoraria, Research Funding; Sanofi: Consultancy, Research Funding; Celgene: Honoraria.

Introduction Histiocytic neoplasms are rare disorders of the monocyte-macrophage-dendritic cell lineage that pose significant management challenges to the clinicians. Over the last five years, there has been emerging data on the role of MAPK/ERK pathway (RAS-RAF-MEK-ERK) in their pathogenesis. In this study, we report the molecular alterations among patients with histiocytic neoplasms seen at our institution. Methods We pursued target-capture next generation sequencing (NGS) on tissue specimen of patients with various histiocytic neoplasms- Erdheim-Chester disease (ECD), Langerhans cell histiocytosis (LCH), Rosai-Dorfman disease (RDD), histiocytic sarcoma (HS), and Langerhans cell sarcoma (LCS). We used three NGS platforms, Tempus® xO (1,714 genes), Tempus® xT (596 genes), or Foundation One® CDX (324 genes). All platforms used formalin-fixed paraffin-embedded tumor tissue specimens for detection of substitutions, insertion and deletion alterations, and copy number alterations, and gene rearrangements. The Tempus assays also utilized matched blood or saliva samples for germline DNA sequencing in addition to whole-transcriptome RNA sequencing. The tumor cellularity threshold for pursuing RNA sequencing was 30% so the test was not pursued specimens for lower cellularity. Results We included 31 cases with histiocytic neoplasms in this study. The disease distribution was as follows: ECD (n=6), LCH (n=7), RDD (n=12), ECD-RDD overlap (n=3), HS (n=2), and LCS (n=1). Among the 13 patients with ECD and LCH, BRAF-V600E mutations were found in 8 (62%) cases. We found several novel DNA alterations in this study in all disease groups: ECD (BRAFV471F), LCH (MAP2K1 in-frame deletion), and RDD (frameshift mutations of DNMT3A, SMARCA4, KMT2A, and CDC73 truncation). In one LCH patient without any DNA alterations, we found MAPK1 and MAP2K1 overexpression on RNA sequencing. We also had two cases with HS, both of which were found to have KRAS exon 3 mutations. One of these cases had concomitant JAK2V617F+ myelofibrosis and the tissue specimen for HS demonstrated TET2 and SRSF2 mutations as well. Our cohort included one patient with multifocal lymph node LCS that demonstrated NRAS and TP53 mutations, who did not respond to MEK-inhibitor therapy. Alterations in epigenetic regulators (TET2, DMNT3A, KMT2A, ASXL1) were found in 5 (16%), potentially suggesting clonal hematopoiesis in a subgroup of histiocytosis. Conclusions Histiocytic neoplasms demonstrate diverse somatic oncogenic alterations. In our study, we noted several novel alterations beyond the MAPK-ERK pathway in RDD that may point toward other potentially pathogenic mechanisms for these rare disorders. In cases where the DNA sequencing does not reveal pathogenic alterations, transcriptome analysis may aid in the diagnosis and management. OffLabel Disclosure: Trametinib use for Langerhans cell sarcoma

Abstract Background: Waldenström macroglobulinemia (WM) is an indolent B-cell lymphoma with a heterogeneous disease course. For nearly a decade, the International Prognostic Scoring system (IPSS), requiring 5 variables (platelet count, hemoglobin, age, Beta 2 microglobulin and immunoglobulin M size) has been used to prognosticate patients with active WM. In this study, we attempt to propose a simplified prognostic model for patients with active/symptomatic WM. Methods: All patients with active WM diagnosed between 01/01/1996 and 12/31/2017 and evaluated consecutively at Mayo Clinic, Rochester were included in the study after Institutional Review Board approval. Active WM was defined as ≥10% marrow infiltration with lymphoplasmacytic cells plus monoclonal IgM of any size requiring systemic therapy. The follow up and overall survival (OS) were calculated from the time of active WM until date of last follow up or death. Baseline parameters at active disease were used to assess prognostic factors for OS using a univariate followed by a multivariate (MV) Cox regression analysis. Independent variables on the MV analysis were given a score proportional to their risk ratios (RR). All time-to-event analyses were performed using the Kaplan-Meier method and the survival curves were compared using log-rank test. Discriminatory ability of the IPSS and the currently proposed prognostic system was assessed using Harrell's concordance index wherein a higher c-statistic is associated with a better discriminatory ability. Results: We identified 889 patients with active WM. The median follow up was 8.2 years (95% CI: 7.5-9 years). The baseline characteristics of the patients are shown in Table 1. At the time of diagnosis of WM, 16% of patients had previously documented MGUS and 16% patients had smoldering (asymptomatic) WM. The course of WM was complicated by systemic amyloidosis in 8% (n=69), transformation to high-grade lymphoma in 4% (n=38), symptomatic hyperviscosity in 13% (n=118), myelodysplastic syndrome in 2% (n=17) and Bing-Neel syndrome in 1.4% (n=12) of patients. Of the patients tested, cryoglobulinemia was present in 17% (n=48), cold agglutinin disease in 34% (n=43) and Coombs positive hemolytic anemia in 9% (n=34) patients. The median OS was 10.6 years (95% CI: 9.7-11.4 years). The factors affecting OS are shown in Table 2. While the patients' MYD88L265P mutation status was not found to be prognostic for OS, age >65 years [RR 1.8 (95% CI: 1.2-2.8); p=0.01], LDH > upper limit of normal [RR 2.5 (95% CI: 1.3-4.6); p=0.003] and serum albumin <3.5 g/dL [RR 1.6 (95% CI: 1.1-2.5); p=0.02] were independently prognostic. Owing to comparable RRs, each of these were assigned a score of 1 point and a prognostic model with a minimum score of 0 and maximum score of 3 was constructed. A score of 0 was considered as low risk WM and 1 as intermediate risk WM. The patients with scores of 2 and 3 were analyzed together to form the high risk cohort due to comparable OS for these two groups. The patient outcomes based on this prognostic model are depicted in Figure 1. Using the new prognostic model (n-=341), the median OS for the low risk group (n=71, 21%) was 14.6 years (95% CI: 9 years- not reached) compared to 11 years (95% CI: 8.1-14.7 years) for intermediate risk (n=140, 41% ) and 7.2 years (95 % CI: 5.4-10 years) for the high risk group (n=130, 38%), p<0.0001. The data for the IPSS-WM were available in 319 patients in the entire cohort. The OS for low risk IPSS (n=56) was 14.6 years (95% CI: 12.1 years-NR), 15.6 years (95% CI: 8.3-18.5 years) for intermediate risk IPSS (n=131) and 9.1 years (95% CI: 6.8-11.2 yeas) for the high risk IPSS group (n=132; p=0.009). Among the 220 patients having data for IPSS-WM as well as our proposed model, the current three variable model held its prognostic significance (p=0.0004). The Harrell's c-index was 0.647 (95% CI 0.592-0.702) for our prognostic model and 0.58 (95%CI: 0.521-0.638) for IPSS-WM. Common frontline treatment comprised of rituximab monotherapy (n=277, 33%), rituximab with alkylator or purine analog combination (n=255, 30.5%) and other therapies, including alkylators/purine analog monotherapy, ibrutinib, proteasome inhibitors, etc., in 37% patients. Conclusion: A simpler, clinically useful, risk stratification model based on age, serum albumin and serum LDH with a potentially higher discriminatory value than IPSS-WM may be used to prognosticate patients with WM. This model requires external validation. Disclosures Ansell: Pfizer: Research Funding; Affimed: Research Funding; Celldex: Research Funding; Bristol-Myers Squibb: Research Funding; Takeda: Research Funding; Trillium: Research Funding; Seattle Genetics: Research Funding; LAM Therapeutics: Research Funding; Merck & Co: Research Funding; Regeneron: Research Funding. Dispenzieri:Celgene, Takeda, Prothena, Jannsen, Pfizer, Alnylam, GSK: Research Funding. Gertz:Abbvie: Consultancy; Prothena: Honoraria; Medscape: Consultancy; annexon: Consultancy; Amgen: Consultancy; Alnylam: Honoraria; Teva: Consultancy; janssen: Consultancy; Physicians Education Resource: Consultancy; Ionis: Honoraria; spectrum: Consultancy, Honoraria; celgene: Consultancy; Research to Practice: Consultancy; Apellis: Consultancy. Witzig:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Lacy:Celgene: Research Funding. Dingli:Millennium Takeda: Research Funding; Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.; Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.; Millennium Takeda: Research Funding. Kumar:Takeda: Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Roche: Research Funding; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding. Kapoor:Takeda: Research Funding; Celgene: Research Funding.

Abstract Introduction Waldenstrom macroglobulinemia (WM) is a rare disease accounting for only 1-2% of all hematologic malignancies and with an overall annual, age-adjusted incidence of approximately 3.5 to 5.5 cases per million-person years. With approximately 13,000 active hematologist/oncologists in the US, most of who are in the community oncology setting, it's estimated that a hematologist/oncologist will only diagnose a WM case approximately every 8 years. Therefore, the clinical experience of a general hematologist/oncologist in the management of WM is likely very limited compared to more prevalent malignances. Previous studies in the setting of rare cancers suggest a correlation between higher volume of care and improved outcomes. Therefore, we explored the volume-outcome relationship in WM using the National Cancer Data Base (NCDB). Methods Patient-level data from the NCDB, a nationwide, facility-based, database covering approximately 70% of all newly diagnosed cancer cases in the US, was queried for all new WM cases diagnosed between 2004 and 2014. Only patients requiring treatment were included. Treatment facilities were divided into quartiles based on the average annual volume of newly diagnosed cases of WM seen. Cox regression was used to analyze the association between facility WM volume and survival, adjusted by demographics (sex, age, race), socioeconomic status (income, education, insurance type), geography (area of residence, treatment facility type, travel distance), comorbidity factors (Charlson-Deyo score), and year of diagnosis. Time-to-event analysis was calculated from frontline therapy initiation date using the Kaplan-Meier method and the log-rank test. Results A total of 3,732 patients with WM treated in 831 facilities were included. The median age at diagnosis was 70 years and 75% of the patients were treated within 20 miles from their residency zip code. Patient characteristics per treatment facility volume quartile are shown in table 1. The median annual facility volume was 1 new WM patient/year (range 0.1 to 21). The median follow-up from frontline treatment was 5 years. The unadjusted median OS by facility volume was: Q1: 6.5 years (95% CI: 5.7-7.4), Q2: 7 years (95% CI: 6.3-8.2), Q3: 8.2 years (95% CI: 7.1-8.9), and Q4: NR (95% CI: 8.5-NR), p<0.0001 (figure 1). The estimated 5-year OS by facility volume was: Q1: 56%, Q2: 61%, Q3: 64%, Q4: 71%, p<0.0001. Multivariate analysis including all variables showed in Table 1 demonstrated that facility volume was independently associated with all-cause mortality. Compared to patients treated at Q4 facilities, patients treated at lower-quartiles facilities had a higher incremental risk of death (Q3 hazard ratio [HR], 1.07 [95% CI: 0.88 to 1.29] p=0.46; Q2 HR, 1.34 [95% CI: 1.11 to 1.63] p=0.002; Q1 HR, 1.52 [95% CI: 1.23 to 1.88] p=<0.0001). Conclusion Our results suggest that a volume-outcome relationship exits in WM as patients treated initially at higher-volume facilities had a lower risk of mortality. Although differences in the underlying disease biology, referral patterns after initial therapy, or cumulative treating-physician experience could not be assessed, these potential biases would only underestimate the magnitude of the volume-outcome relationship reported. Disclosures Ansell: Celldex: Research Funding; Trillium: Research Funding; Takeda: Research Funding; Regeneron: Research Funding; Pfizer: Research Funding; Affimed: Research Funding; Merck & Co: Research Funding; Bristol-Myers Squibb: Research Funding; Seattle Genetics: Research Funding; LAM Therapeutics: Research Funding. Gertz:Medscape: Consultancy; janssen: Consultancy; Alnylam: Honoraria; Ionis: Honoraria; Physicians Education Resource: Consultancy; Prothena: Honoraria; Teva: Consultancy; Research to Practice: Consultancy; spectrum: Consultancy, Honoraria; celgene: Consultancy; Amgen: Consultancy; Abbvie: Consultancy; annexon: Consultancy; Apellis: Consultancy. Kapoor:Takeda: Research Funding; Celgene: Research Funding. Ailawadhi:Amgen: Consultancy; Janssen: Consultancy; Pharmacyclics: Research Funding; Celgene: Consultancy; Takeda: Consultancy. Reeder:Affimed: Research Funding. Witzig:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Dispenzieri:Celgene, Takeda, Prothena, Jannsen, Pfizer, Alnylam, GSK: Research Funding. Lacy:Celgene: Research Funding. Kumar:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding.

Abstract Background The survival of patients with multiple myeloma (MM) has improved significantly over the past two decades with the introduction of novel treatment agents. However, MM is still largely considered an incurable malignancy with a relapsing-remitting course. A follow-up of at least 10 years from active disease is required to determine whether a plateau in progression-free survival has been attained. Prior literature has used 10 years as a cutoff for "long-term survivorship". In this study, we have assessed the biological disease characteristics and outcomes of long-term survivors with MM (≥10 years from active disease). Methods All patients with active MM evaluated at the Mayo Clinic, Rochester between January 1, 1999 and July 1, 2008 were included in the study after approval of the Institutional Review Board. Patients with smoldering multiple myeloma were excluded. The overall survival (OS) was calculated from the time of symptomatic disease requiring treatment. Patients were then divided into two cohorts: (1) long-term survivors, which included patients who had an overall survival of at least 10 years; and (2) short-term survivors, which included patients who had an overall survival of less than 5 years from the diagnosis of active MM. The baseline characteristics between these two groups were compared using Wilcoxon, chi-square, and Fisher's exact test as applicable. All time-to-event analyses were performed using the Kaplan-Meier method and the survival curves were compared using Log-Rank test. Results During the time frame of the study, 2,125 patients were identified who fulfilled the diagnostic criteria for active MM. The median follow-up for the entire cohort was 12.6 years (95% CI: 12.5-13.4).The median OS for the entire cohort was 4.4 years (95% CI: 4.2-4.7 years). Three-hundred and ninety nine (18.7%) patients survived at least 10 years whereas 872 patients (41%) survived less than 5 years from the date of initial diagnosis. The median OS was 14.1 years for the long-term survivors (95% CI: 13.9-14.6 years) and 2.1 years for the short-term survivors (95% CI: 1.8-2.2 years). The clinical features at diagnosis comparing long-term survivors and short-term survivors are shown in Table 1. Among long-term survivors (n=399), based on the available data regarding remission and ongoing treatment status, 331 patients were categorized into 6 cohorts (Table 2). The MM specific survival data of these 6 cohorts is depicted in Table 2.Figure 1 shows survival outcomes from the 10-year landmark. Of the 6 cohorts, 38 patients in Cohort 1 and 19 patients in Cohort 2 (total 57; 17% of long term survivors, ~3% of the entire cohort ) have been off therapy for at least 5 years and remain in remission, representing a distinct group of patients with 100% 15-year survival. Conclusion In our large database with prolonged follow-up, long-term survivors appear to have distinct baseline characteristics, but also constitute a heterogenous group of patients with disparate outcomes. A small subset (17% of long-term survivors) was identified that may represent patients closest to being considered as 'operationally cured'. Disclosures Lacy: Celgene: Research Funding. Dispenzieri:Celgene, Takeda, Prothena, Jannsen, Pfizer, Alnylam, GSK: Research Funding. Gertz:Teva: Consultancy; spectrum: Consultancy, Honoraria; Medscape: Consultancy; Physicians Education Resource: Consultancy; Amgen: Consultancy; Apellis: Consultancy; Alnylam: Honoraria; Abbvie: Consultancy; janssen: Consultancy; celgene: Consultancy; Prothena: Honoraria; annexon: Consultancy; Ionis: Honoraria; Research to Practice: Consultancy. Dingli:Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.; Millennium Takeda: Research Funding; Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.; Millennium Takeda: Research Funding. Kumar:KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Merck: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Research Funding; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding. Kapoor:Celgene: Research Funding; Takeda: Research Funding.

Abstract Background: Limited data exist regarding histological transformation in patients with Waldenström macroglobulinemia (WM). In this study, we present the disease characteristics, outcomes and risk factors for histological transformation in WM. Methods: Patients with WM seen at Mayo Clinic, Rochester, MN between January 1996 and December 2017 were included. Patients with aggressive non-Hodgkin lymphoma in the setting of WM were considered to have transformation. Univariate analysis for comparing baseline characteristics of transformed versus non-transformed WM was performed using Wilcoxon, Fisher's exact and Chi square tests, as appropriate. Multivariate analysis was performed using logistic regression analysis. Cox proportional hazard method was used to assess the impact on time-to-transformation. All time-to-event analyses were calculated by the Kaplan-Meier method. Results: Of 1014 patients with WM, 42 patients (4.1%) developed histological transformation. The median follow-up for the entire cohort was 9.5 years (95% CI: 8.8-10.5 years). The cumulative probability of transformation was 2.3% at 5 years, 5.3% at 10 years and 8.5% at 15 years from diagnosis of WM, respectively. There was no difference in the 5-year cumulative probability of transformation in patients with WM diagnosed between 1996-2000 (2.1%), 2001-2005 (2.9%), 2006-2010 (2.7%) and 2011-2015 (3.8%), p=0.61.The disease characteristics, laboratory parameters and histology at transformation are outlined in Table 1. In patients with DLBCL histology (n=39), Revised-International Prognostic Index was calculable in 28 patients, with 50% (n=14), 46% (n=13) and 4% (n=1) of DLBCL belonging to poor, good and very good risk groups, respectively. For DLBCL histology, 18 patients were classifiable using Hans algorithm into germinal center B-cell (GCB) type (n=3, 17%) and non-GCB type histology (n=15, 83%). The median lines of therapy received prior to transformation for the entire cohort was 2 (range 0-9), with 5 (11%) patients not having received any therapy for WM before transformation. Number of lines of alkylator-based therapy used prior to transformation [median 1 line (range 0-4)] was comparable to that used in patients in whom WM did not occur [median 1, (range 0-6); p=0.78]. The median time-to-transformation from diagnosis of WM was 4.8 years (95% CI: 2.6- 6.8 years). Overall survival (OS) from transformed disease was 3.2 years (95% CI 1.1-3.9 years). The 10-year OS of patients with WM who transformed was lower (46%) compared to patients without transformation (60%) with a trend towards statistical significance (p=0.08), Figure 1. The MYD88L265P mutation status was available in 333 patients in the entire cohort (22/42 pts in the transformed cohort and 311/972 in the non-transformed cohort. Of the 22 patients in the transformed WM cohort, 13 (59%) exhibited MYD88WT genotype and 9 (41%) exhibited MYD88L265P genotype. The risk of transformation was higher in patients with MYD88WT status [Odds ratio 6.3 (95% CI: 2.6-15.5); p<0.0001]. Additionally, serum lactate dehydrogenase (LDH) was higher at diagnosis of WM in patients who transformed, Table 2. On multivariate analysis, MYD88WT status remained an independent predictor of disease transformation [p=0.003; odds ratio 10 (95% CI: 2.1-48)]. On univariate Cox proportional hazard analysis for identifying predictors of time-to-transformation, only MYD88WT mutational status was associated with shorter time-to-transformation with a 5-year transformation rate of 15.5 % for MYD88WT versus 2.6 % with MYDL265P mutated patients [risk ratio 6.2 (95% CI: 2.5-16.4); p<0.0001]. Treatment-related details in the transformed cases were available for 37 (90%) patients; R-CHOP was the most common (41%) frontline therapy for transformation; 33% patients underwent autologous stem cell transplantation for transformed disease during their disease course. Conclusion: Histological transformation is an uncommon event in WM but confers poorer survival. MYD88WT genotype is independently associated with histological transformation a shorter time-to- transformation in patients with WM. Disclosures Ansell: Trillium: Research Funding; Pfizer: Research Funding; LAM Therapeutics: Research Funding; Seattle Genetics: Research Funding; Affimed: Research Funding; Takeda: Research Funding; Celldex: Research Funding; Regeneron: Research Funding; Merck & Co: Research Funding; Bristol-Myers Squibb: Research Funding. Gertz:Apellis: Consultancy; Alnylam: Honoraria; spectrum: Consultancy, Honoraria; janssen: Consultancy; annexon: Consultancy; Prothena: Honoraria; Abbvie: Consultancy; Amgen: Consultancy; celgene: Consultancy; Teva: Consultancy; Medscape: Consultancy; Ionis: Honoraria; Research to Practice: Consultancy; Physicians Education Resource: Consultancy. Dingli:Millennium Takeda: Research Funding; Millennium Takeda: Research Funding; Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.; Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.. Witzig:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Dispenzieri:Celgene, Takeda, Prothena, Jannsen, Pfizer, Alnylam, GSK: Research Funding. Lacy:Celgene: Research Funding. Kumar:Merck: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees; Novartis: Research Funding; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding. Kapoor:Takeda: Research Funding; Celgene: Research Funding.

Abstract Introduction Recent advances in the understanding of the WM pathobiology led to the expansion of our therapeutic options in this disease. A number of targeted drugs are either available or under investigation and are poised to change the chemo-immunotherapy paradigm in the treatment of WM. Now more than ever, an individualized treatment approach for patients with WM is possible, where patient characteristics and preferences can be matched by different treatment goals and side effect profiles. While deep responses have been associated with longer disease-free survival in other hematologic malignancies, data on patients with WM are sparse. We report the impact of depth of response in disease-free and overall survival (OS) in WM. Methods WM patients consecutively seen at Mayo Clinic between 01/1998 and 12/2016 were reviewed for response to therapy and disease burden. The best response achieved after the treatment of interest (TOI) was classified using the IWWM-7 Response Criteria. The included TOI were: BR, DRC, BDR and high-dose chemotherapy followed by ASCT. All time-to-event analyses were performed from the TOI initiation date using the Kaplan-Meier method and the log-rank test. A landmark analysis from the date-of-best response was also performed for OS to prevent immortal-time bias. Univariate and multivariate analyses of progression-free survival (PFS) and time-to-next therapy (TTNT) were performed using the Cox regression method. Results A total of 181 patients had disease response assessed after the TOI. Baseline characteristics at time of diagnosis are summarized in table 1. The median follow up from TOI was 3.8 years (95% CI: 3-4), the majority of patients received TOI as salvage therapy [n=112 (63%); median 2nd line (rage 1-11)]. Best response rates with the corresponding 5-year PFS and TTNT are summarized in table 2. The median OS from TOI was longer in patients who achieved at least a PR [median 7.2 years (95% CI: 5-NR) vs 3.7 years (95% CI: 1.6-NR), p=0.01]. A trend towards a longer OS was also seen with deeper responses (PR or better) achieved with frontline therapy [median 5.8 years (95% CI: 5.8-NR) vs 3.4 years (95% CI: 1.6-NR), p=0.24]. Figure 1 shows the correlation between deeper responses with PFS and TTNT. Among patients achieving a PR or VGPR, those with a normal FLC ratio post TOI demonstrated a longer PFS and TTNT [PFS: median NR (95% CI: 3.4-NR) vs 4.9 years (95% CI: 2.8-8.7), p=0.01; TTNT: median NR (95% CI: 3.5-NR) vs 5.2 years (95% CI: 4.2-9.4), p=0.04], figure 2. In a multivariate analysis including normal FLC ratio, normal IgM level and minimal BM involvement (<5%) post TOI, normal FLC ratio remained an independent prognostic factor for longer PFS and TTNT. Similar trends were seen when considering treatment naïve and relapsed/refractory patients independently (data not shown). Discussion Our results not only suggest an association between depth of response with PFS and TTNT, but also with OS in patients with WM. A normal FLC ratio (not part of the IWWM-7 response criteria) seems to predict a longer disease-free interval in patients achieving a PR or VGPR. Disclosures Gertz: Ionis: Honoraria; Apellis: Consultancy; annexon: Consultancy; Prothena: Honoraria; janssen: Consultancy; Physicians Education Resource: Consultancy; Alnylam: Honoraria; Teva: Consultancy; spectrum: Consultancy, Honoraria; Medscape: Consultancy; celgene: Consultancy; Research to Practice: Consultancy; Amgen: Consultancy; Abbvie: Consultancy. Kapoor:Takeda: Research Funding; Celgene: Research Funding. Ailawadhi:Amgen: Consultancy; Janssen: Consultancy; Takeda: Consultancy; Pharmacyclics: Research Funding; Celgene: Consultancy. Reeder:Affimed: Research Funding. Witzig:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Dispenzieri:Celgene, Takeda, Prothena, Jannsen, Pfizer, Alnylam, GSK: Research Funding. Lacy:Celgene: Research Funding. Kumar:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding. Ansell:Seattle Genetics: Research Funding; Celldex: Research Funding; Bristol-Myers Squibb: Research Funding; LAM Therapeutics: Research Funding; Trillium: Research Funding; Pfizer: Research Funding; Takeda: Research Funding; Merck & Co: Research Funding; Affimed: Research Funding; Regeneron: Research Funding.

Abstract Background : Ibrutinib, a Bruton's tyrosine kinase (BTK) inhibitor was approved for the treatment of Waldenstrom Macroglobulinemia (WM) in January, 2015 based on the results of a clinical trial of 63 previously-treated patients with WM. Data on outcomes with ibrutinib outside of clinical trials are limited. Methods : Medical records of patients with WM seen consecutively between 02/01/2015 and 06/01/2018 at Mayo Clinic, MN, FL and AZ were reviewed and those treated with ibrutinib at any point during their disease were included. Refractoriness to prior therapy was defined as disease progression on therapy or within 2 months of stopping treatment. The response rates were assessed by WM VI International Workshop Criteria. Adverse events were graded using National Cancer Institute Common Toxicity Criteria for Adverse Events (AEs) v4.03. All time-to-event analyses were performed from the time of initiation of ibrutinib. Results : Eighty patients [previously treated, n=67 (84%), treatment-naïve, n=13 (16%)] received ibrutinib for active WM. Median follow-up was 18 months (95% CI: 12-19) and the median overall survival (OS) was not reached (NR) (95% CI: 27-NR) for the entire cohort at the date of last follow-up. The median age was 67 years (range: 50-88) and the median ECOG performance score was 1 (range: 0-3) at the time of ibrutinib initiation. Median lines of therapies prior to ibrutinib for the previously-treated patients was 2 (range: 1-9) and 35 patients (44%) had received ≥3 prior lines of therapy. Of the 80 patients, 52 patients (43 previously treated, 9 treatment-naïve) had data for response assessment. The baseline characteristics and laboratory parameters at initiation of ibrutinib are outlined in Table 1a and prior therapies are mentioned in Table 1b. Overall response rate (ORR) was 90% (100% in patients with ibrutinib as primary therapy and 88% in salvage therapy setting); major-response rate (MRR) was 77%. Median time to first and best response was 2.1 months (95% CI: 1.5-3.5) and 5.4 months (95% CI: 3.5-13), respectively. Other clinically relevant endpoints and AEs related to ibrutinib therapy are outlined in Table 2 and 3, respectively. The median time-to-next therapy was 33 months (95% CI: 28-NR). At last follow-up, 25 (32%) patients had discontinued ibrutinib therapy. The reasons for discontinuation was progression (n=8), elevated liver enzymes (n=4), cognitive changes (n=1), inability to achieve better than MR (n=1), atrial fibrillation (n=3), consolidation with autologous stem cell transplantation after PR with ibrutinib (n=1), transition to hospice care due to progressive head and neck cancer (n=1), infection in lower extremity (n=1), transformation to DLBCL (n=1), blistering rash which resolved after ibrutinib discontinuation (n=1), obscure GI bleed that resolved after ibrutinib discontinuation (n=1), fatigue (n=1) and for unclear reasons recorded as treatment intolerance (n=1). Following discontinuation of ibrutinib, 21 patients received salvage therapy. Of these, data regarding the response to salvage therapy was available in 9 (43%) patients (VGPR=2, PR=3, SD=3 and progressive disease=1); median PFS from the salvage therapy following ibrutinib discontinuation was 18 months (95% CI: 2-25). Of the 4 patients who were not treated following ibrutinib discontinuation; 1 elected hospice care due to concurrent head and neck cancer progression, and the other 3 patients elected to be monitored off therapy (one had achieved SD and two had PR from ibrutinib). Fourteen patients were evaluable for IgM rebound following ibrutinib discontinuation. Of those, 5 (36%) had sudden increase in IgM level [median: 158% from the IgM level after ibrutinib discontinuation (range: 22%-1368%)] within a median of 2 months (range: 1-3 months) and 1 patient required plasmapheresis for symptomatic hyperviscosity. Four of 5 patients received salvage therapy between 0-15 months. At last follow-up, 11 patients (14%) had died of whom 3 were on ibrutinib at the time of death [CNS involvement, (n=1), causes unrelated to WM, (n=2)]. Conclusions : Ibrutinib is an effective agent in WM patients with MYD88L265Pmutation. Our data regarding outcomes in non-trial setting appear comparable to the results observed in the pivotal clinical trial. Hematologists should be aware of unique ibrutinib associated toxicities and clinically relevant IgM rebound phenomenon following abrupt discontinuation of ibrutinib. Disclosures Ailawadhi: Celgene: Consultancy; Janssen: Consultancy; Takeda: Consultancy; Pharmacyclics: Research Funding; Amgen: Consultancy. Gertz:janssen: Consultancy; Prothena: Honoraria; Medscape: Consultancy; Teva: Consultancy; celgene: Consultancy; annexon: Consultancy; Alnylam: Honoraria; Physicians Education Resource: Consultancy; spectrum: Consultancy, Honoraria; Apellis: Consultancy; Amgen: Consultancy; Abbvie: Consultancy; Ionis: Honoraria; Research to Practice: Consultancy. Kumar:Novartis: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Roche: Research Funding; AbbVie: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Oncopeptides: Membership on an entity's Board of Directors or advisory committees; Takeda: Membership on an entity's Board of Directors or advisory committees; KITE: Membership on an entity's Board of Directors or advisory committees, Research Funding; Merck: Membership on an entity's Board of Directors or advisory committees, Research Funding. Lacy:Celgene: Research Funding. Dispenzieri:Celgene, Takeda, Prothena, Jannsen, Pfizer, Alnylam, GSK: Research Funding. Witzig:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Dingli:Millennium Takeda: Research Funding; Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.; Alexion Pharmaceuticals, Inc.: Other: Participates in the International PNH Registry (for Mayo Clinic, Rochester) for Alexion Pharmaceuticals, Inc.; Millennium Takeda: Research Funding. Kapoor:Celgene: Research Funding; Takeda: Research Funding.