Citations

7515 Background: Primary refractory disease (PRD) and early relapse (ER) are predictors of poor prognosis in classic Hodgkin lymphoma (cHL). In this multicenter retrospective study, we describe outcomes of PRD and ER in pts with relapsed/refractory (R/R) cHL treated with salvage therapy (ST) and autologous stem cell transplant (ASCT). Methods: Of 14 sites, adult patients with R/R cHL who received ST and underwent ASCT were enrolled. PRD was defined as progression on frontline chemoimmunotherapy or within 6 months of diagnosis. ER was defined as relapse from 6 months-1 yr of diagnosis. Pts who relapsed >1 yr of diagnosis were called late relapses (LR). Study objectives were Overall response rates (ORR), CR rates, PFS, and OS. Results: Of 986 total pts, 160 had PRD, 365 had ER and 461 had LR. Significantly higher number of pts with PRD, but not ER, had bulky disease (41% vs 27%, p<0.01) and B symptoms (53% vs 38%, p<0.001) than LR. Higher proportions of pts with PRD and ER required >1 line of ST (44% vs 30% vs 23%, p<0.001) before ASCT and received BV maintenance (25% vs 24% vs 16%, p<0.05). When adjusted for B symptoms and Bulky disease, PRD and ER had significantly lower ORR (65% vs 76% vs 84%, p<0.001) and CR (37% vs 46% vs 57%, p<0.001) to first ST than LR. Pts with PRD and ER had significantly lower PFS (56.3%, 61.4%, vs 77.6%, p<.0001) and OS (93% vs 89% vs 94%, p=0.01) than LR. In pts with ER, Brentuximab/bendamustine (BBV) and brentuximab vedotin/nivolumab (BV/nivo) had a trend towards higher ORR (92% vs 92% vs 75%) but significantly higher CR (79.2% vs 76% vs 42%, p<0.01) than platinum based chemotherapy (PBC). In pts with PRD, BBV and BV/Nivo had a statistically insignificant trend towards higher ORR and CR than PBC. The table shows 2 yr PFS by type of ST in PRD, ER, LR. There was no difference in PFS by time to relapse in BV/nivo, CPI and miscellaneous agents. BV/Nivo had a significantly higher PFS than PBC in PRD (88% vs 48%, p<0.05) and ER (95% vs 57%, p<0.05). There was no difference in PFS of PBC and other ST in PRD, ER or LR. OS was not significantly associated with type of ST in either group. Conclusions: PRD and ER are associated with lower response to ST and survival after ASCT compared to late relapse. In pts with PRD and ER, BV/Nivo has high ORR and CR and leads to significantly higher PFS comparable to pts with late relapse and may be preferable ST regardless of time to relapse. [Table: see text]

7514 Background: The AETHERA trial demonstrated improvement in PFS with 16 cycles of brentuximab vedotin (BV) after autologous stem cell transplant (ASCT) in BV-naive patients with high-risk relapsed/refractory classical Hodgkin lymphoma (r/r cHL). However, in real world, patients are rarely able to complete all 16 cycles of BV at full dose. We performed a multicenter retrospective study to assess the impact of cumulative dose on toxicity and 2-year PFS. Methods: Patients from 11 institutions across the US who had received at least one cycle of BV maintenance after ASCT for r/r cHL with one of these features were included: primary refractory disease (PRD), extra-nodal disease (END), or relapse < 12 months of diagnosis (RL<12). PFS was compared between the three cohorts based on a total cumulative dose of 28.8 mg/kg (1.8 mg/kg x 16 cycles): C1, those that received >75% (21.7 to 28.8 mg/kg) cumulative dose of BV, C2, those that received between 51% -75% (14.5 to 21.6 mg/kg) dose and C3, those that received ≤ 50% (≤ 14.4 mg/kg) dose. Results: Between July 2015-June 2019, 100 patients with a median age of 34 years (19-70) underwent ASCT for r/r cHL. At relapse, 44% had PRD, 47% had RL<12, 39% had END and 45% had received BV as initial (1%) or salvage (44%) therapy. 71% had CR before ASCT and 23% received >1 line of salvage (>1 SLT). There was no difference in baseline characteristics between the cohorts. Thirty-six patients were in C1, 27 in C2, and 37 in C3. Only 14% of patients received full cumulative dose of BV. The median number of cycles completed was 12. Fifty-seven patients discontinued early: 39 for toxicity, 7 for progression, 5 for patient preference, 2 for cost and 4 for other reasons. Six of the patients who stopped early for progression were in C3. Grade ≥3 adverse events for neuropathy, neutropenia, and infections were 16%, 7%, and 5% respectively. There was no difference in severity of neuropathy in patients who had received BV prior to ASCT (p=.37). The median follow up was 3.37 years (.4–6.35). The 2-year PFS was 85% for all subjects, 94% for C1, 84% for C2, and 72% for C3 (p=.079) (Table). Patients in C3 had worse PFS compared to C1 (p=.035); this difference remained significant after adjusting for five other factors. There was no difference in PFS between C1 and C2 (p=.29). Conclusions: The majority of patients discontinued BV maintenance early due to toxicity. 2-year PFS was robust regardless of cumulative dose of BV. We conclude that total cumulative dose of 28.8 mg/kg of BV maintenance is not necessary and 51%-75% of total BV dose may still attain a similar PFS advantage. [Table: see text]

Abstract Langerhans cell histiocytosis (LCH) can affect children and adults with a wide variety of clinical manifestations, including unifocal, single-system multifocal, single-system pulmonary (smoking-associated), or multisystem disease. The existing paradigms in the management of LCH in adults are mostly derived from the pediatric literature. Over the last decade, the discovery of clonality and MAPK-ERK pathway mutations in most cases led to the recognition of LCH as a hematopoietic neoplasm, opening the doors for treatment with targeted therapies. These advances have necessitated an update of the existing recommendations for the diagnosis and treatment of LCH in adults. This document presents consensus recommendations that resulted from the discussions at the annual Histiocyte Society meeting in 2019, encompassing clinical features, classification, diagnostic criteria, treatment algorithm, and response assessment for adults with LCH. The recommendations favor the use of 18F-Fluorodeoxyglucose positron emission tomography-based imaging for staging and response assessment in the majority of cases. Most adults with unifocal disease may be cured by local therapies, while the first-line treatment for single-system pulmonary LCH remains smoking cessation. Among patients not amenable or unresponsive to these treatments and/or have multifocal and multisystem disease, systemic treatments are recommended. Preferred systemic treatments in adults with LCH include cladribine or cytarabine, with the emerging role of targeted (BRAF and MEK inhibitor) therapies. Despite documented responses to treatments, many patients struggle with a high symptom burden from pain, fatigue, and mood disorders that should be acknowledged and managed appropriately.

AbstractErdheim–Chester disease (ECD) is a histiocytic neoplasm that predominantly harbors mitogen‐activated protein kinase (MAPK) pathway variants. MAPK inhibitors typically are effective treatments, but mutations outside the MAPK pathway, such as CSF1R variants, may cause refractory ECD. We describe a patient with a novel somatic mutation in CSF1R (CSF1RR549_E554delinsQ) that resulted in refractory ECD affecting the central nervous system. Cell model studies, RNA sequencing analysis, and in silico protein modeling suggested that she had a gain‐of‐function mutation occurring in a region critical for autoinhibition. The patient was treated with pexidartinib, a CSF1R inhibitor, and has had a complete clinical and metabolic response lasting more than 1.5 years to date. To our knowledge, this is the first report to describe successful treatment of a patient with ECD by using an agent that specifically targets CSF1R. This case also highlights the critical role of individualized molecular profiling to identify novel therapeutic targets in ECD.

Abstract Introduction Histiocytic disorders pose significant diagnostic and management challenges for the clinicians due to diverse clinical manifestations and often non-specific histopathologic findings. Herein, we report the tumor board experience from the first-of-its-kind Histiocytosis Working Group (HWG). Materials and Methods The HWG was established in June 2017 and consists of experts from 10 subspecialties that discuss cases in a multidisciplinary format. We present the outcome of tumor board case discussions during the first 2 years since its inception (June 2017-June 2019). Results Forty cases with a suspected histiocytic disorder were reviewed at HWG during this time period. Average number of subspecialties involved in HWG case discussion was 5 (range, 2-9). Histiocytosis Working Group tumor board recommendations led to significant changes in the care of 24 (60%) patients. These included change in diagnosis (n = 11, 27%) and change in treatment (n = 13, 33%). Conclusion Our report highlights the feasibility of a multidisciplinary tumor board and its impact on outcomes of patients with histiocytic disorders.

Abstract Background: Activation of extracellular-signal regulated kinase (ERK) is almost universal in histiocytic disorders and is driven by genomic alterations in the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinases (PI3K) pathways. While BRAFV600E mutations are well described in histiocytic disorders, less is known about BRAF fusions. The goal of our study is to describe the frequency and clinical characteristics of patients harboring BRAF fusions. Methods: We included patients with a diagnosis of histiocytic disorder seen at our institution from November 2016-June 2021. Only those who had adequate BRAF testing were included. The following were considered adequate BRAF testing: 1) unequivocally positive BRAF V600E immunostain with or without molecular confirmation; 2) successful multigene next generation sequencing (mostly Tempus â or FoundationOne â) if BRAF V600Eimmunostain was equivocal or negative. We also searched the literature for similar cases and compared BRAF fusions found in histiocytic disorders to those found in solid tumors and other hematologic conditions. Results: One hundred and twenty-six patients were included in this study. BRAF fusions were detected in 7 (6%) patients. The median follow-up for these patients was 1.4 years (95% CI: 0.4-not reached). The frequency according to disease subtypes is as follows: Erdheim-Chester disease (ECD; 2/46 [4%]), Langerhans cell histiocytosis (LCH; 1/41 [2%]), adult or juvenile xanthogranuloma (AXG/JXG; 4/7 [57%]), and histiocytic or Langerhans cell sarcoma (HS/LCS; 0/9 [0%]). The median age at diagnosis for our study cohort was 34 years (range, 7-81 years) and 5 were females. The clinical characteristics and nature of BRAF fusions of our 7 patients plus additional 13 cases from the literature are shown in Table 1. For the final cohort of 20 patients with BRAF-fusions, the median age was 16 years (range, 0.5-81 years) and most (56%) were females. The distribution by histiocytic subtypes is as follows: AXG/JXG (45%), LCH (40%), ECD (10%), HS/LCS (5%). Two patients received cobimetinib as frontline treatment in our cohort and achieved partial responses. Of these two patients, one completed 12 cycles (12 months) of cobimetinib and had a sustained PR while the other patient received 2 cycles before having to hold therapy due to intolerable adverse effects despite dose reduction. From literature review, another patient (LR-12) received cobimetinib as second line treatment and achieved complete response. We found 15 unique BRAF gene fusions with 4 being recurrent. Except for AGAP3-BRAF, none of these BRAF fusions in histiocytosis has been reported in solid tumors or hematologic conditions to date. Conclusions: BRAF gene fusions occur rarely (&lt;5%) in histiocytic disorders. The only exception is AXG/JXG where more than half of the patients harbor BRAF gene fusions. These gene fusions are mostly distinct to histiocytosis and not found in solid tumors or other hematologic conditions. Figure 1 Figure 1. Disclosures Bennani: Purdue Pharma: Other: Advisory Board; Daichii Sankyo Inc: Other: Advisory Board; Kyowa Kirin: Other: Advisory Board; Vividion: Other: Advisory Board; Kymera: Other: Advisory Board; Verastem: Other: Advisory Board.

Abstract Background: Erdheim-Chester disease (ECD) is characterized by multi-organ infiltration of clonal histiocytes bearing activating mutations predominantly in the MAPK pathway. The diagnosis of ECD is clinico-pathologic; histopathologic findings alone are often non-specific. Characteristic pathognomonic finding of ECD is the symmetric osteosclerosis of the distal femur and proximal tibia/fibula, seen in &gt;90% of cases, and referred to herein as classic ECD (C-ECD). There is a paucity of data on the phenotypic and mutational differences between C-ECD and non-classic ECD (NC-ECD). Determining phenotypic patterns may allow for earlier suspicion and diagnosis. Methods: Patients who met the revised ECD criteria proposed by Haroche J et al (Blood 2020;135:1311-1318) and had full body imaging that included the lower legs (18-FDG-PET/CT or CT/bone scan) were included. ECD diagnosis was made when &gt;1 major criteria plus &gt;1 minor criteria were present. Major criteria: 1) symmetric meta-diaphyseal osteosclerosis in legs; 2) "hairy kidneys"; "coated aorta", right atrial pseudotumor, xanthelasma, exophthalmos; or osteosclerosis of paranasal sinuses. Minor criteria: 1) histologic finding of typical foamy histiocytes (CD68+/CD163+/CD1a-) associated with fibrosis; 2) mutation/gene fusion of BRAF, CSF1R, or MAPK/PI3K pathways. We compared the organ involvement and BRAF V600Emutational status between C-ECD and NC-ECD. Results: A total of 105 patients were included. The median age at diagnosis was 57 years (range, 38-81) and most were males (62%). Majority had 18-FDG-PET/CT (83%) and BRAF V600E testing (65%). The main organ systems involved were skeletal (83%), renal (64%), adrenal (44%), and pulmonary (42%). Central diabetes insipidus (DI), "hairy kidneys", and "coated aorta" were present in 27 (26%), 54 (51%), and 44 (42%) patients, respectively. Among those tested, BRAF V600E mutation was found in 48/67 (72%) by immunohistochemistry. In our cohort, most patients (n=87. 83%) had C-ECD. NC-ECD had significantly lower number of organs/systems involved compared with C-ECD (median 3 vs 6, p=0.002). C-ECD had significantly higher rates of involvement of paranasal sinuses (51%/7%, p=0.002), DI (26%/0%, p=0.02), and similar rates of lung (44%/43%), cardiac (34%/14%), and skin (14%14%) involvement when compared to NC-ECD. BRAF V600E was significantly more common in C-ECD (88%/30%, p=0.004). Thirty-nine (37%) patients underwent next generation sequencing, of whom 33 (31%) had successful testing. In C-ECD, 3 patients had mutations other than BRAF V600E, these included: NRAS, MAP2K1, and MEF2C-FLT3 fusion. In NC-ECD, 5 patients had mutations other than BRAF V600E, these included: MAP2K1, KRAS, and NF1. Conclusions: Our study suggests distinct differences in clinical presentation and molecular findings exist between C-ECD and NC-ECD. C-ECD has a higher degree of organ involvement and harbor BRAF V600E more frequently than NC-ECD. Further analysis of histopathologic findings and outcomes in this cohort may provide insights into these ECD subsets that can optimize future management of this disease. Figure 1: Sites of involvement of classical Erdheim-Chester Disease (C-ECD) versus non-classical Erdheim-Chester Disease (NC-ECD) Figure 1 Figure 1. Disclosures Vassallo: Bristol-Myers-Squibb: Research Funding; Sun Pharma.: Research Funding; Pfizer: Research Funding. Tobin: Mayo Clinic Center for MS and Autoimmune Neurology: Research Funding; Mallinckrodt Pharmaceuticals: Research Funding; National Institutes of Health: Research Funding. Bennani: Verastem: Other: Advisory Board; Purdue Pharma: Other: Advisory Board; Vividion: Consultancy, Other: Advisory Board; Daichii Sankyo Inc: Other: Advisory Board; Kyowa Kirin: Other: Advisory Board.

Abstract Background Histiocytic disorders are rare hematologic neoplasms characterized by their high clinical heterogeneity. Evidence of constitutive activation of the mitogen-activated protein kinase (MAPK) pathway in a number of these disorders has led to the increasing use of BRAF- and MEK-inhibitors as a therapeutic strategy. Response to these therapies is not universal and additional effective treatment options are required. Immune checkpoint inhibitors have proven effective for a wide array of malignancies. Tumor mutational burden (TMB), the total number of somatic pathogenic variants per coding region in a tumor genome, is a clinical biomarker associated with response to immunotherapy. We have previously reported preliminary findings of low TMB in a small cohort of patients with histiocytic neoplasms (Goyal G et al. Blood 2019). In this study, our aim was to confirm the findings in a larger clinical cohort using next generation sequencing studies. Methods A retrospective review of adult patients consecutively seen at Mayo Clinic from 2017 to April 2021 and diagnosis of a histiocytic neoplasm was performed. Electronic records were queried for demographic and laboratory data of all patients who consented to undergo tumor-tissue next-generation sequencing with the Tempus-xT ® or xO ® assay (Chicago, IL), throughout the course of their evaluation. TMB was reported as the number of nonsynonymous mutations per coding area of a tumor genome. TMB across groups was compared via an independent-samples T-test or via analysis of variance and post hoc subgroup testing via Turkey's Test as required. Results Seventy-three patients were included in the study. Individual diagnoses included: Erdheim-Chester disease (ECD) in 31.5% (n=23), including 3 patients with overlap features of ECD and other histiocytoses; Rosai Dorfman disease (RDD) in 28.8% (n=21); Langerhans cell histiocytosis in 21.9% (n=16), histiocytic sarcoma (HS) in 5.5% (n=4), and other histiocytic neoplasms in 12.3% (n=10) including adult xanthogranuloma, xanthoma disseminatum, undifferentiated histiocytoses, and one case of Langerhans cell sarcoma. Median tumor percentage on analyzed samples was 30% (range 10%-90%) and was ≤20% in 29 samples. TMB was &lt;1.0 mutations per megabase (mpMb) in 42.5% (n=31) and &gt;5.0 mpMb in only 6 cases. Median TMB was 1.58 (range 0 - 5.26) for ECD, 1.08 (range 0 - 6.3) for LCH, 0.2 (range 0 - 5.8) for RDD, 3.19 (range 1.67 - 6.8) for HS, and 1.6 (range 0 - 7.5) for other histiocytic neoplasms (Figure 1). No clear association between increasing TMB and number of systems with histiocytic infiltration was observed (Figure 2). A significant increase in TMB was observed among the 5 cases of sarcoma as compared to the rest of the cohort (p=0.014). When not considering sarcomas, no differences were observed in TMB between patients with ECD, LCH, RDD or other histiocytoses (F=0.775; p=0.512). Conclusion In this large cohort of histiocytic disorders, TMB was low compared to that historically seen in other neoplasms though this is likely influenced by tumor purity ≤20% in 29 cases. Only 6 tumors had TMB reports with mpMb above the threshold thought to be associated with an increased likelihood of response to PD-1/PDL1-targeted therapies (&gt;5 mpMb). Our results suggest a low likelihood of response among histiocytic disorders using immune checkpoint inhibitors. Further exploration among malignant histiocytoses (HS and Langerhans cell sarcoma) is warranted given our findings of higher TMB compared with other histiocytic neoplasms. Figure 1 Figure 1. Disclosures Bennani: Kymera: Other: Advisory Board; Vividion: Other: Advisory Board; Kyowa Kirin: Other: Advisory Board; Daichii Sankyo Inc: Other: Advisory Board; Purdue Pharma: Other: Advisory Board; Verastem: Other: Advisory Board.