Immune checkpoint inhibitors (ICPis) are a novel class of immunotherapeutic agents that have revolutionized the treatment of cancer; however, these drugs can also cause a unique spectrum of autoimmune toxicity. Autoimmune hemolytic anemia (AIHA) is a rare, but often severe, complication of ICPis. We identified 14 patients from nine institutions across the United States who developed ICPi-AIHA. The median interval from ICPi initiation to development of AIHA was 55 days (interquartile range [IQR], 22-110 days). Results from the direct antiglobulin test (DAT) were available for 13 of 14 patients: 8 patients (62%) had a positive DAT and 5 (38%) had a negative DAT. The median pretreatment and nadir hemoglobin concentrations were 11.8 g/dL (IQR, 10.2-12.9 g/dL) and 6.3 g/dL (IQR, 6.1-8.0 g/dL), respectively. Four patients (29%) had a preexisting lymphoproliferative disorder, and two (14%) had a positive DAT prior to initiation of ICPi therapy. All patients were treated with glucocorticoids, with three requiring additional immunosuppressive therapy. Complete and partial recoveries of hemoglobin were achieved in 12 (86%) and 2 (14%) patients, respectively. Seven patients (50%) were rechallenged with ICPis, and one (14%) developed recurrent AIHA. Clinical and laboratory features of ICPi-AIHA were similar in DAT positive and negative patients. ICPi-AIHA shares many clinical features with primary AIHA; however, a unique aspect of ICPi-AIHA is a high incidence of DAT negativity. Glucocorticoids are an effective first-line treatment in the majority of patients with ICPi-AIHA, and most patients who are rechallenged with an ICPi do not appear to develop recurrence of AIHA. a Long-standing history of leukopenia of unclear etiology, bone marrow biopsy negative for malignancy, and leukopenia believed to be autoimmune in nature. b Received indoximod in combination with ICPi therapy as part of a clinical trial. c R-CHOP, fludarabine (received >3 years prior to development of AIHA), XRT, auto-SCT for treatment of MZL, and cisplatin and etoposide for treatment of NSCLC. d Received nivolumab on a clinical trial after conventional chemotherapy. e 5-FU, oxaliplatin, irinotecan, bevacizumab, panitumumab, regorafenib, and trifluridine/tipiracil. f Received GVAX and cyclophosphamide in combination with ICPi therapy as part of a clinical trial. g Dabrafenib, trametinib for treatment of melanoma, fludarabine (received >3 years prior to development of AIHA), cyclophosphamide, bendamustine, rituximab, obinutuzumab, and ibrutinib for treatment of CLL.

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SummaryThe prevalence and prognostic value of a concomitant diagnosis of symptomatic or asymptomatic multiple myeloma (MM), as defined by the current International Myeloma Working Group (IMWG) criteria, in patients with immunoglobulin light chain amyloidosis (AL), are unknown. We studied 46 consecutive patients with AL who underwent quantification of serum M-protein and clonal bone marrow plasma cells, as well as a comprehensive evaluation for end organ damage by MM. Using standard morphology and CD138 immunohistochemical staining, 57% and 80% of patients were found to have concomitant MM, respectively. Nine patients exhibited end organ damage consistent with a diagnosis of symptomatic MM. While overall survival was similar between AL patients with or without concurrent myeloma (1-year overall survival 68% vs. 87%; P = 0Á27), a diagnosis of symptomatic myeloma was associated with inferior outcome (1-year overall survival 39% vs. 81%; P = 0Á005). Quantification of bone marrow plasma cells by both standard morphology and CD138 immunohistochemistry identified a much higher prevalence of concurrent MM in patients with AL than previously reported. Evaluation of bone marrow plasma cell infiltration and presence of myeloma associated end organ damage could be clinically useful for prognostication of patients with AL.

Cyclic thrombocytopenia (CTP) is a rare disease of periodic platelet count oscillations. The pathogenesis of CTP remains elusive. To study the underlying pathophysiology and genetic and cellular associations with CTP, we applied systems biology approaches to two patients with stable platelet cycling and reciprocal thrombopoietin (TPO) cycling at multiple time points through 2 cycles. Blood transcriptome analysis revealed cycling of platelet-specific genes, which are in parallel with and precede platelet count oscillation, indicating that cyclical platelet production leads platelet count cycling in both patients. Additionally, neutrophil and erythrocyte-specific genes also showed fluctuations correlating with platelet count changes, consistent with TPO effects on hematopoietic progenitors. Moreover, we found novel genetic associations with CTP. One patient had a novel germline heterozygous loss-of-function (LOF) thrombopoietin receptor (MPL) c.1210G>A mutation, and both had pathogenic somatic gain-of-function (GOF) variants in signal transducer and activator of transcription 3 (STAT3). In addition, both patients had clonal T-cell populations that remained stable throughout platelet count cycles. These mutations and clonal T cells may potentially involve in the pathogenic baseline in these patients rendering exaggerated persistent thrombopoiesis oscillations of their intrinsic rhythm upon homeostatic perturbations. This work provides new insights into the pathophysiology of CTP and possible therapies.

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4872 Backgroud Prognosis in AL amyloidosis is commonly viewed as dichotomous, based on the presence or absence of cardiac involvement. Patients with cardiac AL amyloidosis are reported to have a dismal prognosis, with a median survival of approximately 6 months. Furthermore, cardiac involvement is often considered a contraindication to hematopoietic cell transplant. Aims To compare the prognosis of patients with cardiac AL amyloidosis with and without presenting symptoms of congestive heart failure (CHF). Methods The study population consisted of individuals with biopsy-proven AL amyloidosis and cardiac involvement seen at the Stanford University Amyloid Center. Cardiac involvement was defined by the presence of amyloid deposits on endomyocardial biopsy or the combination of increased ventricular mass with reduced electrocardiographic voltage. Results A total of 27 patients (median age 64 years, 37% female) were evaluated. The 16 patients with CHF symptoms had a median age of 65 years with a median of 2 organs involved with amyloidosis. The 11 patients without CHF symptoms had a median age of 59 years with a median of 3 organs involved. At diagnosis, NT-proBNP was significantly higher in the group with CHF symptoms (15,938 vs. 2,538 pg/ml, P<0.001), as was the likelihood of detectable troponin I (86% s. 36%, P<0.02). Mean levels of the involved serum free light chain (179.7 vs. 47.9 mg/dL) were nonsignificantly higher in the cohort with CHF. Though there was no difference in the mean interventricular septal width between the two groups (1.5 cm), the mean systolic blood pressure (sBP) (91 vs. 115 mm Hg, P<0.001) and left ventricular ejection fraction (45 vs. 59%, p=0.02) were significantly lower in the group with CHF symptoms. A total of 6 patients (4 without CHF symptoms, 2 with CHF symptoms) received hematopoietic cell transplants, and 3 patients received heart transplants. Other therapies employed included oral melphalan (6 patients), dexamethasone (19 patients), lenalidomide (17 patients), and bortezomib (4 patients). After a median follow-up of 24 months, there were 9 deaths in the cohort with CHF symptoms vs. 0 in the group without CHF symptoms. Six-month survival (50% vs. 100%, P<0.01) and one-year survival (42% vs. 100%, P<0.01) were significantly lower in the group with CHF symptoms. Discussion CHF at presentation is the primary factor which predicts a poor prognosis in patients with cardiac AL amyloidosis. In our cohort, no patient without CHF symptoms at diagnosis later developed CHF, and thus new CHF symptoms do not appear to be a typical consequence of progressive disease. Conclusion Not all patients with cardiac AL amylodosis have an exceptionally poor prognosis. Many patients have ‘incidental’ cardiac involvement in the absence of CHF symptoms and appear to do well with both standard and intensive therapies. Disclosures Witteles: Celgene: Research Funding. Off Label Use: Melphalan, lenalidomide & bortezomib as therapy for AL amyloidosis.. Witteles:Celgene: Research Funding. Schrier:Celgene: Research Funding.

Introduction: The development of immune checkpoint inhibitors (ICPis) has ushered in a new paradigm for the treatment of both solid and liquid malignancies. However, these therapies, which promote an activated T cell phenotype, can cause a unique spectrum of autoimmune toxicities known as immune-related adverse events (IRAEs), which can affect a variety of organ systems. Autoimmune hemolytic anemia (AIHA) has been described as a rare complication of ICPis, but existing data are mostly limited to isolated case reports. Further, guidelines for the diagnosis and treatment of these patients are lacking. We describe the clinical and laboratory features of 14 patients who developed ICPi-associated AIHA. Methods: We contacted hematology departments at 18 academic medical centers across the U.S. to inquire about potential cases of ICPi-associated AIHA. Nine centers contributed a total of 14 cases to the current series. We defined AIHA as an abrupt decrease in hemoglobin ≥2g/dL, the presence of at least two laboratory features of hemolysis (elevated serum lactate dehydrogenase [LDH], elevated reticulocyte percentage, low or absent serum haptoglobin, and spherocytes), and the exclusion of other causes of anemia. We collected data on demographics and comorbidities, features of AIHA, and response to treatment. We defined complete recovery (CR) and partial recovery (PR) of hemoglobin as an increase from the nadir hemoglobin to within 1 and 2 g/dL of the baseline value, respectively, in the absence of recent transfusion. Results: The clinical features of the 14 patients in our cohort with ICPi-associated AIHA are summarized in the Figure (panel A). Underlying malignancies included melanoma (n = 9), non-small cell lung cancer (n = 3), colorectal cancer (n = 1), and acute myelogenous leukemia (n = 1). Four patients had a pre-existing diagnosis of a lymphoproliferative disorder, and two of these patients were known to have a positive direct antiglobulin test (DAT) prior to initiation of ICPi. ICPis used included ipilimumab, nivolumab, a combination of ipilimumab and nivolumab, and pembrolizumab. Representative hemoglobin and LDH trends are shown in the Figure (panels B and C). The median (interquartile range [IQR]) interval from initiation of ICPis to AIHA was 55 (22-110) days. Eight patients (57%) were DAT positive: 3 were positive for both IgG and C3; 3 were positive for IgG alone; 2 were positive for C3 alone; and 1 was weakly positive on polyspecific testing. Five patients (36%) were DAT negative, and in one patient a DAT was not performed. The median (IQR) hemoglobin nadir was 6.3 (6.1-8.0) g/dL,and 11 patients (79%) required red blood cell transfusion. All patients were treated with glucocorticoids, with 3 requiring additional immunosuppressive therapy. All patients achieved a CR or PR of hemoglobin in response to treatment (CR, n = 11; PR, n =3). The median (IQR) time from the hemoglobin nadir to CR or PR was 47 (30-62) days. Seven patients (50%) experienced at least one other IRAE. Seven patients (50%) were re-challenged with ICPis, and one patient developed recurrent AIHA with re-challenge. Conclusion: ICPi-associated AIHA is a recently-described phenomenon, which will be encountered more frequently with the widespread use of ICPis. ICPi-associated AIHA shares many clinical features with other forms of AIHA; however, a unique aspect of ICPi-associated AIHA appears to be a relatively high incidence of DAT negativity (36% in our series, compared with 3-11% in other forms of AIHA). It is possible that more advanced DAT testing - i.e., "super-Coombs" - which was not performed in any of the patients in this series, would have yielded different results. Glucocorticoids appear to be an effective first-line regimen in most patients with ICPi-associated AIHA. Furthermore, we found that AIHA does not necessarily recur with ICPi re-challenge. Additional studies are needed to better understand the mechanisms underlying ICPi-associated AIHA and optimal treatment strategies. Disclosures Anagnostou: ASH Research Training Award for Fellows 2018: Research Funding; Mayo Clinic SPORE: Research Funding; Mayo Clinic Immune Monitoring Core: Research Funding; Mayo Clinic Hematology Research Division: Research Funding. Salama:BMS: Research Funding; Celldex: Research Funding; Dynavax: Research Funding; Genentech: Research Funding; Merck: Research Funding; Reata: Research Funding; Incyte: Research Funding; Immunocore: Research Funding; Array: Consultancy; Merck: Consultancy; Biocryst: Consultancy; BMS: Speakers Bureau.

4044 Background: Conventionally, multiple myeloma is believed to coexist in approximately 10% of AL amyloidosis patients. However, it is unclear whether this figure is too low based on current World Health Organization criteria. These criteria, mainly created to differentiate myeloma from monoclonal gammopathy of undetermined significance, include the presence of ≥ 10% plasma cells on a bone marrow biopsy or aspirate as being diagnostic of myeloma. Aims: To define the frequency and relevance of a concomitant diagnosis of myeloma in patients with AL amyloidosis. Methods: Records from consecutive patients with biopsy-proven AL amyloidosis treated at the Stanford University Amyloid Center were reviewed. Plasma cell percentages were determined by manual counts from bone marrow aspirate smears and by CD138 immunohistochemistry (IHC) performed on bone marrow core biopsies. Results: A total of 41 patients (median age 61 years, 32% female) were evaluated. The median number of organs involved with amyloidosis was 2 (range 1–4), with 28 patients (68%) having cardiac involvement, 22 patients (54%) having renal involvement, 15 patients (37%) having gastrointestinal involvement, 12 patients (29%) having soft tissue involvement, and 10 patients (24%) having nervous system involvement. All patients had bone marrow biopsies and aspirates performed at the time of amyloid diagnosis, with most undergoing both manual counts of plasma cells from aspirates and IHC from core biopsies. Based on conventional criteria, manual aspirate counts defined 15/28 (54%) patients as having myeloma, and IHC defined 26/31 (84%) patients as having myeloma (p=0.01). Only nine patients had a detectable serum paraprotein on immunofixation (median 1.1 g/dl, range 0.4–2.6). 81% of patients had an elevated serum free light chain (85% lambda), with a median level of 37.3 mg/dl (range 8.6–256 mg/dl). Compared to the frequency of elevated plasma cells, the prevalence of anemia (29%), hypercalcemia (14%), impaired kidney function (21%), and lytic lesions (7%) was low. After a median follow-up of 13 months (range 1–127 months), the one-year overall survival (74% vs. 58%) and three-year overall survival (50% vs. 50%) was not significantly different between patients with ≥10% plasma cells and patients with <10% plasma cells (p=NS). Discussion: As defined by bone marrow plasma cell involvement, a strikingly high percentage (84%) of AL amyloidosis patients would be considered to have concurrent myeloma. This figure is much higher than has been traditionally quoted in the literature, likely due to the utilization of newer methods of counting plasma cells. There was a low prevalence of myeloma-associated end-organ effects (hypercalcemia, anemia, renal insufficiency, lytic bone lesions), and a myeloma diagnosis had no impact on survival. Conclusion: In this cohort of AL amyloid patients, concomitant myeloma was present in the vast majority of patients using modern diagnostic techniques. The significance of this diagnosis appears to be minimal – calling into question whether the diagnostic criteria for myeloma should be redefined in this population. Disclosures: Witteles: Celgene: Research Funding. Liedtke:Celgene: Lecture fee, Research Funding. Schrier:Celgene: Research Funding.