Porrata, Luis F.

7623 Background: Survival for patient with primary CNS lymphoma (PCNSL), in general, is poor with patients requiring frequent chemotherapy treatments or receiving whole-brain radiation therapy, which can potentially result in significant neurologic decline and dementia. Because of the improved survival of high risk patients with aggressive lymphoma undergoing autologous stem cell transplant (ASCT), we began ASCT for patients with PCNSL in first or later remission with chemotherapy sensitive disease. We now report on outcomes of patients who have had at least 1 year follow up post ASCT. Methods: Between June, 2000 and September, 2004, 11 patients underwent ASCT for PCNSL. The medical records of consenting patients were abstracted for the following information. Median age at transplant was 47 years old (range 30–67). Median number of prior treatments 1 (range 1–3). Median time from diagnosis to transplant was 7.5 months (range 2.9 to 75.8). Median International Extranodal Working Study Group Prognostic Score: 2 (range 0–3). Disease status at transplant: First CR 5 patients, later CR or PR 6 patients. Results: Eleven patients underwent ASCT for PCNSL and have a minimum of 1 year follow-up. All patients received BEAM conditioning. Median follow up was 28.3 months. Four patients have relapsed at a median of 200 days (range 40–523). Of the patients who relapsed, one has died of disease progression and the remaining three are alive after additional therapy. Median overall survival and progression free survival from transplant have not been reached. Two year overall and event free survival are 89% and 61%, respectively. Conclusions: Although limited by patient selection and retrospective biases, this review suggests that ASCT for PCNSL demonstrates improved overall survival when compared to historical controls with similar PCNSL Prognostic Scores (2 year survival for patients from diagnosis with PS 2–3 was 48% in a prior published study). ASCT in first remission in patients with PCNSL appears promising and may limit the need for additional therapy which can be myelosuppressive or result in neurologic decline. No significant financial relationships to disclose.

7605 Background: In the setting of autologous stem cell transplantation (ASCT) in multiple myeloma (MM), it has been shown that peripheral blood absolute lymphocyte count (ALC) on day 15 is an independent prognostic factor for clinical outcomes. Recently the International Staging System (ISS) for MM has been developed as a simple staging system to assess survival in newly diagnosed MM patients. The role of ALC on survival in newly diagnosed MM patients is unknown. Methods: Between 1994 and 2002, 1,835 consecutive MM patients were evaluated at the Mayo Clinic, Rochester. Of these patients, we retrospectively analyzed 584 MM patients that were originally diagnosed and followed at the Mayo Clinic. The primary end point was to assess the role of ALC at the time of MM diagnosis on overall survival (OS). OS was measured from the date of diagnosis to time of death or last follow-up. ALC was analyzed as a continuous variable and dichotomized based on finding the optimal cut point based on the log-rank statistic. ALC was then compared to the ISS. Results: The median age of the cohort was 67 years (range: 29–94 years), including 234 females and 350 males. The median follow-up was 32 months (range: 1–136 months). The median ALC at diagnosis was 1.2 x 109/L (range: 0.12–5.44 x 109/L). ALC, as a continuos variables was identified as a prognostic factor for OS (HR= 0.466, 95%CI= 0.396–0.547, p < 0.0001). MM patients with an ALC ≥ 1.3 x 109/L experienced a superior OS compared with MM patients with an ALC < 1.3 x 109/L (55.5 months versus 22.6 months, p< 0.0001). In the multivariate analysis, ALC was independent prognostic factor when compared to the ISS (HR = 0.580, 95%CI=0.518–0.647, p< 0.0001). Conclusions: Our study shows that ALC at diagnosis for MM is an independent prognostic factor for OS, suggesting how the host immune status plays a critical role in the survival of patients with MM. No significant financial relationships to disclose.

7586 Background: The immunologic mechanisms of action of rituximab have been described as complement mediated lysis, vaccine like effect, antibody-dependent cellular cytotoxicity (ADCC) and the cellular microenvironment. We hypothesized that in the treatment of follicular grade 1 lymphoma (FL), the presence of a stronger host immune status prior to rituximab therapy would result in a prolonged time to progression (TTP). As a surrogate marker for immune status, we evaluated the absolute lymphocyte count (ALC) prior to rituximab treatment. Methods: Between 1996 and 2002, 1,104 consecutive FL patients were evaluated at Mayo Clinic Rochester. Of these patients, we retrospectively analyzed a group of all FL patients who received rituximab (375 mg/m2 once a week for four weeks) alone at any time during their lymphoma treatment at the Mayo Clinic (n=79). The primary end-point was to assess the impact of ALC just prior to rituximab therapy on TTP for FL. Results: The median age of the cohort was 56.6 years (range: 25–98 years). The median follow-up was 12.5 months (range: 1–76 months). An ALC count of ≥ 890 cells/μL prior to rituximab therapy predicted a longer TTP compared with an ALC < 890 cells/μl (25 months versus 8 months, respectively, p < 0.0124). A higher complete response rate was observed in the ALC ≥ 890 cells/μL group compared with the ALC < 890 cells/μL group [15/40 (38%) vs 5/39 (13%), p < 0.035]. The groups were balanced regarding the Follicular Lymphoma International Prognostic Index (FLIPI) (p = 0.794). Multivariate analysis demonstrated ALC ≥ 890 cells/μL prior to rituximab therapy as an independent prognostic factor for TTP when compared to hemoglobin, LDH, and Ann Arbor stage. The ALC was independent of the FLIPI in multivariate analysis. Conclusions: This data supports the hypothesis that a higher lymphocyte count, as a marker of the immune status of the patient, predicts for a longer TTP following rituximab therapy. No significant financial relationships to disclose.

18505 Background: Besides radiation, the immunologic mechanisms of action of 90Y ibritumomab tiuxetan (Zevalin) radioimmunotherapy (RIT) have been attributed to complement mediated lysis and antibody-dependent cellular cytotoxicity (ADCC). We hypothesized that a stronger host immune system prior to Zevalin therapy for relapsed follicular (grade 1&2) lymphomas (FL) would result in an improved time to progression (TTP). As a surrogate marker of host immune status, we studied absolute lymphocyte count (ALC) prior to Zevalin therapy and its impact on TTP in relapsed FL patients. Methods: Between 1996 and 2006, 75 patients with relapsed FL were treated with single agent Zevalin (0.4 mCi/kg, maximum of 32 mCi) at the Mayo Clinic. ALC was obtained from the complete blood cell count prior to RIT. Results: The median age of the cohort was 60 years (range, 29–82 years). 36% (27/75) patients were rituximab refractory. The median TTP in all patients was 6.4 months (range, 1–99+ months). Univariately, ALC as a continuous (HR = 0.448, p < 0.006) or dichotomized [ALC = 1.0 x 109/l (HR = 0.684, p < 0.007)] variable was identified as a prognostic factor for TTP. Superior TTP was observed with an ALC = 1.0 x 109/l (N = 32) compared with an ALC < 1.0 x 109/l (N=43) (median: 12.4 months vs 6.5 months, respectively, p < 0.007). Both groups were balanced in regard to the Follicular Lymphoma International Prognostic Index (FLIPI). ALC, as a continuous (HR = 0.507, p < 0.02) or dichotomized [ALC = 1.0 x 109/l (HR = 0.697, p < 0.01)] variable was identified as an independent prognostic factor for TTP in the multivariate analysis when compared with FLIPI. In the ALC = 1.0 x 109/l group, 14/32 (44%) of FL patients achieved a TTP = 12 months compared to only 7/43 (16%) in the ALC < 1.0 x 109/l group, (p < 0.02). Conclusions: This study supports our hypothesis that a higher ALC, as a marker of immune status of the patient, predicts longer TTP following Zevalin therapy in relapsed FL. No significant financial relationships to disclose.

8055 Background: mTOR inhibition with intravenous temsirolimus (Wyeth Pharmaceuticals) has been associated with responses in mantle cell lymphoma (J Clin Oncol 23;5347, 2005) as well as other lymphomas (Blood 108 (11) 2483; 2006). This phase II study tested the oral mTOR inhibitor everolimus (RAD001, Novartis Pharmaceuticals) in three simultaneous two-stage phase II lymphoma studies - aggressive (group 1), indolent (group 2), or uncommon (group 3). The goals were to learn the toxicity profile and to assess the anti-tumor response. Planned interim analysis for groups 1 and 3 have been completed and are the subject of this report. Methods: Patients (pts) received 10 mg PO daily for each 28 day cycle (up to 12) and restaged after 2, 6, and 12 cycles. The primary endpoint is the confirmed response rate, including CR, CRu or PR. 12 pts were enrolled in stage 1 of each study. At least 1 success in 12 is required to proceed to stage 2, to a total of 37 pts. Overall, the treatment will be considered promising if 4 or more successes are observed in all 37 pts in each group. Results: The median age of the 12 pts in group 1 was 68.5 yrs (range: 53–80), with a median of 3 (range, 1–15) prior therapies. Four pts had a prior stem cell transplant (SCT). Pts completed a median of 7 (range, 1–12) cycles of therapy. 6 confirmed responses have been achieved (1 CR, 5 PR), meeting the overall criteria for promising results in this study. Common grade 3 adverse events (AEs) include thrombocytopenia (3 pts) and anemia (2 pts). For group 3, the median age was 49 yrs (range, 27–78), with a median of 7 (range, 1–13) prior therapies and 6 pts had a prior SCT. Pts have completed a median of 6.5 cycles (range, 1–11). 5 confirmed responses have been achieved (5 PR), meeting the criteria for this regimen to be considered promising. Of these 5 patients, 3 had HD, 1 T-cell NHL, and 1 had macroglobulinemia. Common grade 3 AEs include anemia (3 pts) and thrombocytopenia (2 pts). No grade 4 AEs were reported. Conclusions: Oral everolimus has activity in a spectrum of lymphomas with acceptable toxicity. The responses observed in both group 1 and group 3 met the criteria to continue accrual. These results provide the rationale for additional studies with this novel class of agents and to integrate mTOR inhibitors into salvage treatment regimens. No significant financial relationships to disclose.

Abstract Background - The phenotype and biological role of monocytes in B-cell non-Hodgkin lymphoma (NHL) is not fully understood, however, an increased absolute monocyte count in the peripheral blood of lymphoma patients is associated with a poor prognosis. We have previously reported that monocytes from patients with relapsed B-cell NHL displayed an immunosuppressive CD14+HLA-DRlow/- phenotype that correlated with a poor prognosis. However, the underlying mechanism by which CD14+HLA-DRlow/- monocytes develop in patients with B-cell NHL is unknown. The goal of this study was to determine whether cytokines are responsible for the increased number and phenotype of CD14+HLA-DRlow/-monocytes present in lymphoma patients. Methods – Whole blood from patients with newly diagnosed, untreated B-cell NHL (n=20) and healthy donors (n=20) was stained with a panel of antibodies and analyzed by 10-color flow cytometry. Cytokine levels in serum and culture supernatants were measured by Luminex and ELISA, respectively. Polarization of monocytes from healthy donors was performed by incubating CD14+ cells with specific cytokines or supernatants from B-cell NHL cell lines for 24 hours. Activation and proliferation of CD4+T cells cocultured with IL-10-pretreated monocytes were measured by flow cytometry. Results – By flow cytometry, we observed that the absolute number of peripheral monocytes was increased in newly-diagnosed lymphoma patients compared to healthy donors. A significant proportion of these monocytes displayed an immunosuppressive CD14+HLA-DRlow/- phenotype and the numbers of CD14+HLA-DRlow/- cells were significantly higher in lymphoma patients than in healthy donors. To identify the underlying mechanism by which CD14+HLA-DRlow/- monocytes develop thereby leading to increased numbers of CD14+HLA-DRlow/- monocytes in B-cell NHL, we tested a panel of cytokines and found that IL-10 played a key role in the process. Firstly, treatment of monocytes with IL-10 in vitro resulted in the generation of CD14+HLA-DRlow/- cells. Second, monocytes co-cultured with IL-10 producing lymphoma B-cells, or treated with supernatants from lymphoma cell cultures, developed a CD14+HLA-DRlow/- phenotype. Thirdly, IL-10 levels were increased in the serum of DLBCL (p<0.0001) and FL patients (p=0.010) compared to healthy controls, and serum IL-10 levels correlated with increased numbers of peripheral monocytes (p=0.02). Finally, IL-10-pretreated CD14+HLA-DRlow/- monocytes were significantly immunosuppressive and inhibited the proliferation and activation of CD4+T cells in co-culture assays. Conclusions- Taken together, our results suggest that IL-10 signaling contributes to the increased numbers of CD14+HLA-DRlow/- monocytes in B-cell NHL. Strategies to inhibit IL-10 production may therefore have therapeutic potential in B-cell NHL. Disclosures No relevant conflicts of interest to declare.

Abstract Introduction New treatment strategies are improving outcomes for patients with Hodgkin (HL) and non-Hodgkin lymphoma (NHL) but achieving durable responses and cure in the relapsed patient remain a challenge. Both the mTORC1 inhibitor everolimus (RAD001) and the IMiD, lenalidomide (LEN) have efficacy as single agents in patients with relapsed and refractory (R/R) HL and NHL. Individually, LEN and RAD present a low toxicity profile and in combination may offer synergistic therapeutic efficacy by unique mechanisms of action. A phase I/II clinical trial of RAD and LEN was designed to explore the tolerability, toxicity and to determine the maximum tolerated dose (MTD) of this combination for the Phase II study. The results of phase I/II data are reported here. Methods MC0981 was activated on January 10, 2011. In phase I, the study enrolled a total of 25 patients and RAD 5 mg daily + LEN 10 mg/d X 21d in a 28-day cycle was defined as the MTD. The phase II opened on May 14, 2013, and closed on Feb 19, 2014, during which 33 patients were enrolled and were treated until progression of disease. Eligibility required age ≥18, biopsy proven relapsed or refractory NHL or HL, ECOG PS 0- 2, measurable disease, Hb >9g/dl, ANC ≥1200/uL, platelet ≥ 50,000/uL, creatinine ≤1.5xULN and willingness to sign informed consent. Women of child bearing potential had pregnancy testing and all patients followed recommendations for contraception. Follow up data was analyzed as of July 2014. Results A total of 58 patients were enrolled to this study and fifty five are evaluable for analysis (2 never started therapy, 1 deemed ineligible). The median age was 62 years (21-82) and 38 (69.1%) were male. Sixty-five percent had stage IV disease and 42% had 4 or more prior treatments including stem cell transplantation in 49%. Histologies included HL (n=10) and NHL (n=45 with 23 DLBCL, 2 FL-III, 5 LPL, 3 MCL, 2 MF, and 3 other). At least 1 Gr≥3 adverse event was seen in 74.5% of patients. The most common Gr≥3 toxicities were hematologic - neutropenia (30.9%), and thrombocytopenia (21.8%), and anemia (10.9%). Nine of 55 patients (16%) had Gr≥3 infection; 2 with skin infection, 1 with cholecystitis, 1 with lung infection, 1 with pharyngitis 1 with otitis externa, 1 with otitis media, and 1 with pleural infection and 1 with upper respiratory tract infection. Seven patients discontinued treatment due to adverse events. At this time, 44% (25/55) remain progression-free. A documented tumor response, as overall response rate (ORR) was seen in 20% (11/55) with 1CR, 8PR, and 2MR; 17 remain on therapy; and 22 deaths have occurred with a median survival of 15.0 months (95% CI 7.5-NR). Median follow up time was 5.5 (range, 0.7- 41.0) months. The median duration of response (DOR) in those responding is 19.4 months. Conclusions In a heavily pretreated population with baseline compromised bone marrow function, the combination of everolimus and lenalidomide is feasible with a modest ORR and a surprisingly long DOR. Future studies in more defined groups of NHL or HL are necessary to better predict which patients will be long-term responders. This trial is sponsored by Novartis and Celgene Disclosures Off Label Use: mTORC1 inhibitor (Everolimus) and the Immunomodulatory (IMiD) drug Lenalidomide for patients with Heavily Pretreated Relapsed Lymphoma . Mikhael:Onyx: Research Funding; Celgene: Research Funding; Sanofi: Research Funding; Novartis: Research Funding. Nowakowski:Celgene, Morphosis: Consultancy. Witzig:Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Research Funding. Reeder:Millennium, Celgene, Novartis: Research Funding.

Background: Central nervous system (CNS) involvement by peripheral T cell lymphoma (PTCL) is a rare condition. Among primary CNS lymphomas, only 2% are secondary to PTCL, while the risk of CNS relapse in all cases of PTCL is estimated at 2% to 6%. Little is known about the presentation and outcomes of PTCL patients with CNS involvement given the rarity of this entity. In this study, we describe patient characteristics, histology, and clinical course of patients with CNS involvement by PTCL. Methods: The Mayo Clinic Lymphoma Database was used to identify PTCL patients with primary or secondary CNS involvement seen at our institution between 2000 and 2018. A total of 12 patients were identified and their medical records were reviewed for patient and disease characteristics, CNS-directed treatment modality, and outcomes. The Kaplan-Meier method was used for time-to-event analysis. Results: The median age at CNS diagnosis was 63 years (range 41 to 76) and 11 (93%) patients were male. The histological diagnoses were PTCL, NOS in 9 (75%) patients, enteropathy-associated T-cell lymphoma in 2 (17%) patients, and angioimmunoblastic T-cell lymphoma in 1 (8%) patient. Five patients presented with primary T-cell CNS lymphoma (all with a PTCL, NOS histology), while the remaining 7 (58%) patients also had systemic involvement. All patients presented with neurologic symptoms at the time of CNS involvement diagnosis including: focal motor deficits in 6 patients (unilateral upper extremity weakness, gait impairments, and hemiparesis), cognitive decline in 5 patients (memory impairments, reduced attention, and confusion), headache in 4 patients, and seizure in 3 patients. The CNS disease location included the brain parenchyma in 9 (75%) patients, leptomeninges in 1 (8%) patient, and lumbar plexus in 1 (8%) patient. One patient (8%) had positive CSF finding only without radiologic evidence of involvement. CSF analysis was performed in 11 patients. Elevated protein levels were noted in 3 (27%) patients, malignant cells in 2 (18%), and no clear abnormalities in the remaining 6 (55%) patients. Concomitant bone marrow involvement was seen in only 1 patient. Elevated LDH was seen in 2 patients. The a median LDH was 195 U/L (range 139 to 4,360) The most common CNS-directed therapies were: high-dose methotrexate (MTX)-based regimens in 8 (67%) patients, including high-dose MTX in combination with temozolomide (n=2), or cytarabine and thiotepa (n=2). Intrathecal MTX, temozolomide and dexamethasone, lenalidomide, high-dose steroids, and surgical resection were the treatment modality used for one patient each. At a median follow up of 18 months, eight (75%) out of 12 patients were not alive at the time of last follow up. The median overall survival (OS) from diagnosis was 16 months (95% CI: 2.8-173). The median progression free survival (PFS) from initiation of CNS-directed therapy was 9 months (95% CI: 1.6-33) (figure). Four patients had a PFS longer than 12 months. These 4 patients were treated with: temozolomide/dexamethasone, high-dose MTX, lenalidomide, and high-dose MTX followed by cytarabine/thiothepa. Conclusion: CNS involvement by T-cell lymphoma is a rare complication that carries a poor prognosis. Early onset of neurologic symptoms should trigger prompt investigation of CNS involvement. Despite the short OS and PFS, some patients may achieve a relatively longer disease free interval. Disclosures Bennani: Adicet Bio: Other: Advisory board; Seattle Genetics: Other: Advisory board; Purdue Pharma: Other: Advisory board; Seattle Genetics: Other: Advisory board; Seattle Genetics: Other: Advisory board; Bristol-Myers Squibb: Research Funding; Bristol-Myers Squibb: Research Funding; Kite Pharma: Other: Advisory board; Kite Pharma: Other: Advisory board; Bristol-Myers Squibb: Research Funding; Adicet Bio: Other: Advisory board; Purdue Pharma: Other: Advisory board; Purdue Pharma: Other: Advisory board; Adicet Bio: Other: Advisory board; Kite Pharma: Other: Advisory board. Cerhan:Celgene: Research Funding; NanoString: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees. Nowakowski:Celgene: Consultancy, Research Funding; Bayer: Consultancy, Research Funding; Curis: Research Funding; F. Hoffmann-La Roche Ltd: Research Funding; Genentech, Inc.: Research Funding; MorphoSys: Consultancy, Research Funding; NanoString: Research Funding; Selvita: Membership on an entity's Board of Directors or advisory committees. Ansell:Mayo Clinic Rochester: Employment; Affimed: Research Funding; Bristol-Myers Squibb: Research Funding; Bristol-Myers Squibb: Research Funding; Regeneron: Research Funding; Trillium: Research Funding; Seattle Genetics: Research Funding; Regeneron: Research Funding; LAM Therapeutics: Research Funding; Trillium: Research Funding; Mayo Clinic Rochester: Employment; Affimed: Research Funding; LAM Therapeutics: Research Funding; Seattle Genetics: Research Funding. Paludo:Celgene: Research Funding; Verily Life Sciences: Research Funding; Verily Life Sciences: Research Funding; Celgene: Research Funding.

Introduction: Front-line immunochemotherapy (IC) with rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) is expected to cure 60-70% of newly diagnosed DLBCL. Up to one third of newly diagnosed DLBCL patients will have relapsed or refractory (r/r) disease.1 Current standard of care for these patients is salvage chemotherapy and, if chemosensitive, to be followed by high dose chemotherapy with hematopoietic cell rescue (autoHCT).2,3 Event-free survival at 24 months (EFS24) after frontline IC is associated with excellent long-term outcomes with overall survival (OS) similar to that of age- and sex-matched controls.4 In comparison, those achieving EFS24 following autoHCT for relapsed or refractory disease may have increased risk for late-mortality compared to the general population with advanced age and intensive salvage therapy contributing to the risk of late complications.5 We sought to better characterize EFS24 after autoHCT to determine the utility of this end-point for informed clinical decisions, patient management, and future clinical trials. Methods: Patients were prospectively enrolled onto the Molecular Epidemiology Resource (MER) of the University of Iowa/ Mayo Clinic Specialized Program of Research Excellence (SPORE). Patients were followed for relapse, retreatment, and death; all events were validated by medical record review. For this analysis patients were included if they were consented within 9 months of initial diagnosis of DLBCL between 2002-2012, had received anthracycline-based IC (R-CHOP, or similar), and eventually had undergone autoHCT for r/r DLBCL. Patients with primary central nervous system (CNS) lymphoma or post-transplant lymphoproliferative disorders (PTLD) were excluded. Overall survival (OS) was defined as time from autoHCT until death due to any cause. Event-free survival (EFS) was defined as time from autoHCT until progression, relapse, retreatment, or death due to any cause. OS from achieving EFS24 after autoHCT was compared to age- and sex-matched general US population. Results: 108 patients underwent autoHCT for relapsed DLBCL between 2002 and 2017. Median age at autoHCT of the patients was 60 years (range 20-78) and 72 (67%) were male. The most common transplant conditioning regimen was BEAM (82%). At a median follow-up after autoHCT of 85 months (range 1-171), 72 patients (67%) had an event and 64 patients (59%) had died. Kaplan-Meier estimates for EFS and OS at 24 months from the time of autoHCT were 49% (95% CI: 40-59) and 61% (95% CI: 52-71), respectively. 52 patients had a progression within 24 months of autoHCT; OS from progression was poor (median OS=2.8 months, 95% CI: 1.8-6.0; 5 year OS = 9%, 95% CI: 2-22). 48 patients achieved EFS24 after autoHCT; median OS from achieving EFS24 was 136 months (95% CI: 92-NE) and 5 year OS was 79% (95% CI: 68-93). This was inferior to the background population (Figure 1, SMR=3.64, 95% CI: 2.11-6.27, p<0.0001). Eight patients had a progression after achieving EFS24 from autoHCT. OS from progression in these 8 patients (median OS=27.3 months, 95% CI: 14.4-NE; 5 year OS = 16%, 95% CI: 3-93) was improved compared to progression within 24 months of autoHCT (p=0.072, figure B). Cause of death (COD) in EFS24 achievers was progression of lymphoma (n=6), infection (n=1), secondary malignancy related to therapy (n=3), heart disease (n=1), and unknown (n=1). Conclusions: Patients achieving EFS24 after salvage chemotherapy and autoHCT have a favorable long-term prognosis; however, overall survival remained inferior to the general population. Most common COD after achieving EFS24 was progression of lymphoma. In spite of this, EFS24 remains a valuable end-point for informed clinical decisions, patient management, and future clinical trials. Figure 1 Disclosures Maurer: Morphosys: Membership on an entity's Board of Directors or advisory committees; Celgene: Research Funding; Nanostring: Research Funding. Ansell:Mayo Clinic Rochester: Employment; Bristol-Myers Squibb: Research Funding; Affimed: Research Funding; Trillium: Research Funding; Regeneron: Research Funding; Seattle Genetics: Research Funding; Mayo Clinic Rochester: Employment; Affimed: Research Funding; Bristol-Myers Squibb: Research Funding; LAM Therapeutics: Research Funding; Regeneron: Research Funding; Seattle Genetics: Research Funding; Trillium: Research Funding; LAM Therapeutics: Research Funding. Cerhan:Celgene: Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; NanoString: Research Funding. Farooq:Celgene: Honoraria; Kite Pharma: 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.