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Key PointsPatients with an abnormal sFLC ratio because of LC suppression have outcomes similar to those with a normal ratio. sFLC ratio has prognostic value in patients achieving CR who have an absence of clonal BMPCs assessed by MFC.

AbstractOur prior studies identified the prognostic significance of quantifying cPCs by multiparametric flow cytometry (MFC) in newly diagnosed multiple myeloma (NDMM) patients. We evaluated if a similar quantification of cPCs could add prognostic value to the current R‐ISS classification of 556 consecutive NDMM patients seen at the Mayo Clinic, Rochester from 2009 to 2017. Those patients that had ≥5 cPCs/μL and either R‐ISS stage I or stage II disease were re‐classified as R‐ISS IIB stage for the purposes of this study. The median time to next therapy (TTNT) and overall survival (OS) for patients with ≥5 cPCs/μL at diagnosis was as follows: R‐ISS I (N = 110) ‐ 40 months and not reached; R‐ISS II (N = 69) ‐ 30 and 72 months; R‐ISS IIB (N = 96) ‐ 21 and 45 months and R‐ISS III (N = 281) ‐ 20 and 47 months respectively. Finally, ≥ 5 cPCs/μL retained its adverse prognostic significance in a multivariable model for TTNT and OS. Hence, quantifying cPCs by MFC can potentially enhance the R‐ISS classification of a subset of NDMM patients with stage I and II disease by identifying those patients with a worse than expected survival outcome.

AbstractHistological transformation in Waldenström macroglobulinemia (WM) is an uncommon complication, with limited data, particularly regarding the impact of MYD88 L265P mutation on transformation. We examined risk factors and outcomes associated with transformation in WM, highlighting the role of MYD88 L265P mutation. Patients with WM seen at Mayo Clinic, Rochester, USA and University Hospital of Reims, France, between 01/01/1996 and December 31, 2017 were included; 50 (4.3%) of 1147 patients transformed to a high‐grade lymphoma, with median time‐to‐transformation of 4.5 (range 0‐21) years in the transformed cohort. The MYD88 L265P mutation status was known in 435/1147 (38%) patients (406 with non‐transformed WM and 29 patients in transformed cohort). On multivariate analysis, MYD88 WT status alone was an independent predictor of transformation (odds ratio, 7[95%CI: 2.1‐23]; P = .003). Additionally, the MYD88 WT status was independently associated with shorter time‐to‐transformation (HR 7.9 [95%CI: 2.3‐27; P = .001]), with a 5‐year transformation rate of 16% for MYD88 WT vs 2.8% with MYD88 L265P mutated patients. Patients with transformation demonstrated a significant increase in risk of death compared to patients who did not transform (HR 5.075; 95%CI: 3.8‐6.8; P < .001). In conclusion, the MYD88 WT status is an independent predictor of transformation and associated with a shorter time‐to‐transformation. Additionally, transformation conferred an inferior overall survival in patients with WM.

BACKGROUND: pPCL is a rare and aggressive form of multiple myeloma (MM) with poor survival outcomes compared to that experienced by MM patients. It has been traditionally defined by the presence of an absolute plasma cell count of > 2000/microL or >20% circulating plasma cells (cPCs) in the peripheral blood. However, several recent studies have validated the optimal cutoff for defining pPCL to be >5% cPCs on a peripheral blood smear due to equally poor outcomes in this less restrictive cohort. Hence, given the rarity of this disease entity, we evaluated the clinical outcomes and cytogenetic features of patients diagnosed with pPCL at our institution with the new proposed definition of pPCL by >5% cPCs on peripheral blood smear that were treated with novel agent induction therapies. METHODS: We evaluated all patients with pPCL diagnosed between 2000 - 2018 evaluated at Mayo Clinic in Rochester, Minnesota. Data regarding these patients were extracted from a prospectively maintained database and from the review of the electronic medical records. Patients were categorized as having high risk cytogenetics if any of the following abnormalities were present: del 17p, t(4;14), t(14;16) or t(14;20). Chi-square tests and Fisher exact tests were used to compare differences between the sub-groups of interest. Survival analysis was performed by the Kaplan-Meier method and differences assessed using the log rank test. RESULTS: This cohort consisted of 71 patients with pPCL with a median age of 62 years (range: 34-91) of which 33 (46%) were male. The median follow up was 46 months (95% CI: 41 - 90). The median bone marrow plasma cell content was 84% (Range: 10 - 100) and the median plasma cell percentage on the peripheral smear was 23% (range: 5 - 93). There were 48 (68%) patients with >20% cPCs in their peripheral blood smear. Only 23 (32%) patients had concurrent information on the number of cPCs by multiparametric flow cytometry at diagnosis and the median number of cPCs detected was 32,807 per 150,000 events analyzed (Range: 354 - 132,256). There were 15/54 (28%) patients who presented with a creatinine of 2 mg/dL or greater and 17/55 (31%) pts who presented with hypercalcemia (11 mg/dL or greater). Data for ISS classification was available in 45 patients and is as follows: Stage 1- 3 (7%) patients, Stage 2- 10 (22%) patients and Stage 3- 32 (71%) patients. Data on the presence of primary cytogenetic abnormalities were available in 60 (85%) patients of which 29 (49%) had high risk cytogenetics. The distribution of primary cytogenetic abnormalities among this cohort was as follows: t(11;14) - 27 (45%), t(4;14) - 5 (8%), t(14;16) - 8 (13%), t(14;20)- 3(5%) and del 17p- 15(25%). All patients received novel agent induction therapy with 40 (57%) of them having received at least one autologous stem cell transplant and 1 patient undergoing an allogeneic stem cell transplant. The median overall survival (OS) for all pPCL patients in this cohort was 23 months (95% CI: 19 - 38). The OS was similar in patient with 5-19% cPCs vs. >20% cPCs (24 vs. 23 months, P = 0.999). However, when the entire cohort was stratified by cytogenetic risk, the median OS was 51 months for standard risk vs. 19 months for high risk (P = 0.005) (FIGURE). There were only 17 (30%) patients in this cohort who were alive for 48 months or longer since diagnosis (i.e. twice the median OS of this cohort) and they were more likely to not have high risk cytogenetics at diagnosis (P = 0.05). CONCLUSION: In this analysis of one of the largest contemporary cohorts of pPCL patients, the outcomes of patients diagnosed with pPCL remain poor despite the use of novel agent induction therapy. However, some patients appear to do better than expected and this phenomenon may be influenced by the absence of high risk cytogenetics. Disclosures Kumar: Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Takeda: Research Funding. Dispenzieri:Akcea: Consultancy; Intellia: Consultancy; Janssen: Consultancy; Pfizer: Research Funding; Takeda: Research Funding; Celgene: Research Funding; Alnylam: Research Funding. Dingli:Karyopharm: Research Funding; Rigel: Consultancy; Millenium: Consultancy; Janssen: Consultancy; alexion: Consultancy. Lacy:Celgene: Research Funding. Kapoor:Glaxo Smith Kline: Research Funding; Sanofi: Consultancy, Research Funding; Amgen: Research Funding; Takeda: Honoraria, Research Funding; Cellectar: Consultancy; Celgene: Honoraria; Janssen: Research Funding. Russell:Imanis: Equity Ownership. Leung:Omeros: Research Funding; Takeda: Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees; Aduro: Membership on an entity's Board of Directors or advisory committees. Gertz:Celgene: Consultancy; Prothena Biosciences Inc: Consultancy; Appellis: Consultancy; Amgen: Consultancy; Springer Publishing: Patents & Royalties; Amyloidosis Foundation: Research Funding; International Waldenstrom Foundation: Research Funding; Janssen: Consultancy; Ionis/Akcea: Consultancy; Alnylam: Consultancy; Annexon: Consultancy; Abbvie: Other: personal fees for Data Safety Monitoring board; Research to Practice: Consultancy; Teva: Speakers Bureau; Medscape: Consultancy, Speakers Bureau; Physicians Education Resource: Consultancy; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Proclara: Membership on an entity's Board of Directors or advisory committees; Spectrum: Consultancy, Research Funding; i3Health: Other: Development of educational programs and materials; Johnson and Johnson: Speakers Bureau; DAVA oncology: Speakers Bureau.

Introduction: Abnormal metaphase cytogenetics are associated with inferior survival in newly diagnosed multiple myeloma (MM). These abnormalities are only detected in one third of cases due to the low proliferative rate of plasma cells. It is unknown if metaphase cytogenetics improve risk stratification when using contemporary prognostic models such as the revised international staging system (R-ISS), which incorporates interphase fluorescence in situ hybridization (FISH). Aims: The aims of this study were to 1) characterize the association between abnormalities on metaphase cytogenetics and overall survival (OS) in newly diagnosed MM treated with novel agents and 2) evaluate whether the addition of metaphase cytogenetics to R-ISS, age, and plasma cell labeling index (PCLI) improves model discrimination with respect to OS. Methods: We analyzed a retrospective cohort of 483 newly diagnosed MM patients treated with proteasome inhibitors (PI) and/or immunomodulators (IMID) who had metaphase cytogenetics performed prior to initiation of therapy. Abnormal metaphase cytogenetics were defined as MM specific abnormalities, while normal metaphase cytogenetics included constitutional cytogenetic variants, age-related Y chromosome loss, and normal metaphase karyotypes. Multivariable adjusted proportional hazards regression models were fit for the association between known prognostic factors and OS. Covariates associated with inferior OS on multivariable analysis included R-ISS stage, age ≥ 70, PCLI ≥ 2, and abnormal metaphase cytogenetics. We devised a risk scoring system weighted by their respective hazard ratios (R-ISS II +1, R-ISS III + 2, age ≥ 70 +2, PCLI ≥ 2 +1, metaphase cytogenetic abnormalities + 1). Low (LR), intermediate (IR), and high risk (HR) groups were established based on risk scores of 0-1, 2-3, and 4-5 in modeling without metaphase cytogenetics, and scores of 0-1, 2-3, and 4-6 in modeling incorporating metaphase cytogenetics, respectively. Survival estimates were calculated using the Kaplan-Meier method. Survival analysis was stratified by LR, IR, and HR groups in models 1) excluding metaphase cytogenetics 2) including metaphase cytogenetics and 3) including metaphase cytogenetics, with IR stratified by presence and absence of metaphase cytogenetic abnormalities. Survival estimates were compared between groups using the log-rank test. Harrell's C was used to compare the predictive power of risk modeling with and without metaphase cytogenetics. Results: Median age at diagnosis was 66 (31-95), 281 patients (58%) were men, median follow up was 5.5 years (0.04-14.4), and median OS was 6.4 years (95% CI 5.7-6.8). Ninety-seven patients (20%) were R-ISS stage I, 318 (66%) stage II, and 68 (14%) stage III. One-hundred and fourteen patients (24%) had high-risk abnormalities by FISH, and 115 (24%) had abnormal metaphase cytogenetics. Three-hundred and thirteen patients (65%) received an IMID, 119 (25%) a PI, 51 (10%) received IMID and PI, and 137 (28%) underwent upfront autologous hematopoietic stem cell transplantation (ASCT). On multivariable analysis, R-ISS (HR 1.59, 95% CI 1.29-1.97, p < 0.001), age ≥ 70 (HR 2.32, 95% CI 1.83-2.93, p < 0.001), PCLI ≥ 2, (HR 1.52, 95% CI 1.16-2.00, p=0.002) and abnormalities on metaphase cytogenetics (HR 1.35, 95% CI 1.05-1.75, p=0.019) were associated with inferior OS. IR and HR groups experienced significantly worse survival compared to LR groups in models excluding (Figure 1A) and including (Figure 1B) the effect of metaphase cytogenetics (p < 0.001 for all comparisons). However, the inclusion of metaphase cytogenetics did not improve discrimination. Likewise, subgroup analysis of IR patients by the presence or absence of metaphase cytogenetic abnormalities did not improve risk stratification (Figure 1C) (p < 0.001). The addition of metaphase cytogenetics to risk modeling with R-ISS stage, age ≥ 70, and PCLI ≥ 2 did not improve prognostic performance when evaluated by Harrell's C (c=0.636 without cytogenetics, c=0.642 with cytogenetics, absolute difference 0.005, 95% CI 0.002-0.012, p=0.142). Conclusions: Abnormalities on metaphase cytogenetics at diagnosis are associated with inferior OS in MM when accounting for the effects of R-ISS, age, and PCLI. However, the addition of metaphase cytogenetics to prognostic modeling incorporating these covariates did not significantly improve risk stratification. Disclosures Lacy: Celgene: Research Funding. Dispenzieri:Akcea: Consultancy; Intellia: Consultancy; Alnylam: Research Funding; Celgene: Research Funding; Janssen: Consultancy; Pfizer: Research Funding; Takeda: Research Funding. Kapoor:Celgene: Honoraria; Sanofi: Consultancy, Research Funding; Janssen: Research Funding; Cellectar: Consultancy; Takeda: Honoraria, Research Funding; Amgen: Research Funding; Glaxo Smith Kline: Research Funding. Leung:Prothena: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding; Omeros: Research Funding; Aduro: Membership on an entity's Board of Directors or advisory committees. Kumar:Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Takeda: Research Funding.

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.

Background: The overall participation of cancer patients in interventional clinical trials in the United States remains very low, with ~5% of patients being enrolled in clinical trials nationwide. The outcomes of patients with MM have improved significantly over the past decade, but available data suggest that the participation rates for patients with MM is comparable to other cancers. The drivers of participation and the potential impact of clinical trial participation have not been systematically studied in MM. Patients and Methods: We identified 228 patients who were enrolled into clinical trials for initial therapy of newly diagnosed MM between 2004 and 2018, and 4 controls for each of these patients. Controls were patients with NDMM, who were diagnosed closest in time to the index patients and did not participate in an interventional treatment trial. Various baseline characteristics as well as overall survival were compared between the two groups. Results: The baseline characteristics of the two groups are as shown in the Table. Patients who entered clinical trials were more likely to be female, resided closer to the clinic, and were more likely to have a prior history of MGUS. They were more likely to have higher ISS Stage, and a higher serum LDH, but there was no difference in the FISH risk status. Other indices of disease burden such as lower hemoglobin and platelets, higher serum creatinine were all seen more often in the control group, but may have been influenced by the trial entry criteria. Looking at the outcomes, the overall survival was longer among those enrolled into clinical trials compared to those who did not [median 103 (95% CI; 86, 136) vs. 63 (95% CI; 53, 69) months, p<0.001 (Figure). Conclusions: The current study provides important clues regarding demographic determinants of trial participation and disease biology related features that reflect likelihood of trial participation. Overall survival was significantly longer among the trial participants, which likely represent a mix of reasons including baseline status of patients, intensity of monitoring and efficacy of novel treatment approaches. Table Disclosures Kapoor: Janssen: Research Funding; Celgene: Honoraria; Cellectar: Consultancy; Sanofi: Consultancy, Research Funding; Amgen: Research Funding; Glaxo Smith Kline: Research Funding; Takeda: Honoraria, Research Funding. Dispenzieri:Alnylam: Research Funding; Janssen: Consultancy; Pfizer: Research Funding; Takeda: Research Funding; Celgene: Research Funding; Akcea: Consultancy; Intellia: Consultancy. Gertz:Ionis: Honoraria; Alnylam: Honoraria; Prothena: Honoraria; Celgene: Honoraria; Janssen: Honoraria; Spectrum: Honoraria, Research Funding. Lacy:Celgene: Research Funding. Dingli:Karyopharm: Research Funding; Rigel: Consultancy; alexion: Consultancy; Janssen: Consultancy; Millenium: Consultancy. Leung:Omeros: Research Funding; Aduro: Membership on an entity's Board of Directors or advisory committees; Takeda: Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees. Russell:Imanis: Equity Ownership. Kumar:Takeda: Research Funding; Janssen: Consultancy, Research Funding; Celgene: Consultancy, Research Funding.

Introduction: There is a paucity of randomized trials to guide therapy for relapsed AL amyloidosis with treatment regimens generally extrapolated from experience in multiple myeloma. Methods: We conducted a retrospective review of patients who relapsed after receiving autologous stem cell transplant at Mayo Clinic. Patients treated for first relapse between January 2004 and December 2018 were included. Results: Three hundred and twenty-one patients were seen for relapsed AL amyloidosis post ASCT during the study period. Baseline characteristics were typical for a cohort with AL amyloidosis and are listed in Table1. 39% received therapy prior to transplant, conditioning in the majority (75%) was melphalan 200mg/m2. The median progression free survival from transplant (PFS1) was 30.7 months. Of the 321 patients 294 received treatment for relapsed disease. We categorized treatment regimens according to commonly used combinations and drug classes to further analyze outcomes. 34 patients were excluded from this analysis as they either proceeded directly to second ASCT (n=10) or received an atypical regimen not commonly considered for AL amyloidosis (n=24). Five categories of therapy regimens were identified, thalidomide based (n=110), melphalan plus steroids (n=31), 2nd generation immunomodulatory (IMiD) drug +/- alkylator (n=76), proteasome inhibitor (PI) +/- alkylator (n=116), PI plus IMiD (n=16), or daratumumab based (n=9). Disease and treatment characteristics for patients treated with these regimens are listed in Table 2. Patients treated with thalidomide had the shortest PFS1 (17.7 months) but PFS1 was similar for those treated with melphalan plus steroids, PI+IMiD and 2nd generation IMiDs (25.5, 24.3 and 25.6 months respectively). Patients treated with a PI +/- alkylator and daratumumab based regimen had the longest PFS1 (36.7 and 41.9 months respectively). The median duration of therapy was longer in patients treated with a 2nd generation IMiD or daratumumab based regimen (10.2, 12, 6.1, 5.5, 6.2 and 5.9 months for Dara based, 2nd generation IMiD, PI+/- alkylator, PI+IMiD, melphalan plus steroids and thalidomide based respectively). Hematologic response rate was lowest in those treated with melphalan plus steroids or thalidomide based regimens (44% and 55% respectively) and highest for patients treated with a PI+/- alkylator, (Figure 1). Progression free survival from relapsed therapy (PFS2) was longest amongst patients treated with daratumumab based regimens, PI +/- alkylator and 2nd generation IMiDs (not reached, 29.9 and 26.7 months respectively), Figure 2A. Overall survival from time of relapsed therapy favored patients treated with daratumumab based regimens, 2nd generation IMiDs and PI +/- alkylator, Figure 2b). Conclusion: A second generation IMiD based regimen or PI +/- alkylator produce high response rates and prolonged progression free and overall survival for relapsed AL amyloidosis. Patients treated with daratumumab based regimens and those treated with a PI plus IMiD also appear to do well, although numbers were low in our study. Patients treated with melphalan plus steroids or thalidomide based combinations have inferior outcomes and these regimens should be avoided. Disclosures Dispenzieri: Celgene: Research Funding; Takeda: Research Funding; Pfizer: Research Funding; Janssen: Consultancy; Intellia: Consultancy; Akcea: Consultancy; Alnylam: Research Funding. Lacy:Celgene: Research Funding. Dingli:Karyopharm: Research Funding; Rigel: Consultancy; Millenium: Consultancy; Janssen: Consultancy; alexion: Consultancy. Leung:Takeda: Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees; Aduro: Membership on an entity's Board of Directors or advisory committees; Omeros: Research Funding. Kapoor:Glaxo Smith Kline: Research Funding; Sanofi: Consultancy, Research Funding; Celgene: Honoraria; Cellectar: Consultancy; Amgen: Research Funding; Takeda: Honoraria, Research Funding; Janssen: Research Funding. Kumar:Takeda: Research Funding; Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding. Gertz:Medscape: Consultancy, Speakers Bureau; Prothena Biosciences Inc: Consultancy; Ionis/Akcea: Consultancy; Alnylam: Consultancy; Celgene: Consultancy; Janssen: Consultancy; Spectrum: Consultancy, Research Funding; Appellis: Consultancy; Amgen: Consultancy; Physicians Education Resource: Consultancy; Abbvie: Other: personal fees for Data Safety Monitoring board; Research to Practice: Consultancy; Teva: Speakers Bureau; Johnson and Johnson: Speakers Bureau; DAVA oncology: Speakers Bureau; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees; Proclara: Membership on an entity's Board of Directors or advisory committees; i3Health: Other: Development of educational programs and materials; Springer Publishing: Patents & Royalties; Amyloidosis Foundation: Research Funding; International Waldenstrom Foundation: Research Funding; Annexon: Consultancy. OffLabel Disclosure: Daratumumab off label use for AL amyloidosis.

Introduction: Daratumumab is a human immunoglobulin (IgG-κ) that targets CD38 abundantly expressed on plasma cells. Data is emerging to show its efficacy as part of induction therapy for newly diagnosed multiple myeloma (MM) patients. Hematopoietic stem cells have been shown to express CD38 on the cell surface and therefore during mobilization, there is a theoretical risk of circulating daratumumab binding to and having downstream effects on these cells. Methods: We conducted a retrospective review of MM patients treated with daratumumab prior to stem cell collection and autologous stem cell transplant (ASCT) to identify any effects daratumumab therapy may have on the efficacy of the stem cells in bone marrow recovery. The study was conducted at Mayo Clinic Rochester from February 2018 to May 2019. Granulocyte colony-stimulating factor was the preferred agent used for stem cell mobilization and plerixafor was added in a demand-adapted fashion. All patients received melphalan infused at day -1 before their ASCT and the decision about dosing (200mg/m2 vs 140mg/m2) was at the physicians' discretion. Neutrophil engraftment was defined as the first date of three consecutive neutrophil counts >0.5 x 10^9/L and platelet engraftment was defined as the first date of three consecutive platelet counts >50 x 10^9/L in the absence of platelet transfusion in the preceding 7 days. Results: We identified 12 patients who received daratumumab as part of their first induction regimen (daratumumab cohort) and compared them to 129 patients who did not receive daratumumab prior to stem cell mobilization and transplant during the study period (no daratumumab cohort). Of the daratumumab cohort, 11 patients received daratumumab, ixazomib, lenalidomide, and dexamethasone and one received daratumumab, cyclophosphamide, bortezomib and dexamethasone. No differences were noted in terms of melphalan dose or the number of CD34+ stem cell infused. The median time from the last dose of daratumumab to stem cell collection was 3.9 weeks. In patients receiving daratumumab, the median time for neutrophil engraftment was three days longer compared with those who did not receive daratumumab (median of 19 days vs. 16 days, P=0.017) (Figure 1, A). Median platelet engraftment was delayed by one day, although this was not statistically significant (median of 18 days vs. 17 days, p=0.12) (Figure 1, B). A total of 6 patients (50%) from the daratumumab cohort and 52 (40%) from the no daratumumab cohort required hospital admission. Of these admissions, there was no difference between the two groups in rates of admission for fever (50% in the daratumumab group vs. 42% in the no daratumumab group, P=0.7). Conclusion: Our case series provides the first report of daratumumab delaying engraftment post transplant in myeloma patients receiving it prior to stem cell collection. A better characterization of this phenomenon is important given the increasing use of daratumumab as front line therapy prior to ASCT in patients with myeloma. Disclosures Gertz: Prothena: Honoraria; Celgene: Honoraria; Janssen: Honoraria; Spectrum: Honoraria, Research Funding; Alnylam: Honoraria; Ionis: Honoraria. Lacy:Celgene: Research Funding. Kapoor:Sanofi: Consultancy, Research Funding; Glaxo Smith Kline: Research Funding; Cellectar: Consultancy; Janssen: Research Funding; Amgen: Research Funding; Takeda: Honoraria, Research Funding; Celgene: Honoraria. Dispenzieri:Alnylam: Research Funding; Celgene: Research Funding; Takeda: Research Funding; Pfizer: Research Funding; Janssen: Consultancy; Intellia: Consultancy; Akcea: Consultancy. Dingli:alexion: Consultancy; Janssen: Consultancy; Millenium: Consultancy; Rigel: Consultancy; Karyopharm: Research Funding. Kumar:Celgene: Consultancy, Research Funding; Janssen: Consultancy, Research Funding; Takeda: Research Funding.