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Abstract Introduction: The real-world outcomes in patients (pts) with PCALCL in the era of targeted therapies like Brentuximab Vedotin (BV) is not well defined due to lack of large multicenter studies. We conducted a multicenter retrospective analysis (RWA) to assess patient and disease characteristics, treatment patterns, survival outcomes and impact of novel therapies in this rare type of cutaneous T cell lymphoma (CTCL). Methods: The analysis included 167 adult (≥18 years) patients (pts) with PCALCL across 9 academic institutions in the United States diagnosed between 01/2012 to 06/2022. The study was approved by the Institutional Review Boards at the respective sites. Demographic and disease factors were summarized using descriptive statistics. Overall survival (OS) and relapse-free survival (RFS) were estimated using Kaplan-Meier method and compared via log rank tests. Prognostic models included factors such as age, sex, race, performance status (PS), disease stage, type of initial lesion, presence of B symptoms, previous history of lymphomatoid papulosis and prior transplant. Prognostic factors for survival were assessed using both univariable and multivariable Cox proportional hazard models. Results: The median age at diagnosis was 61 (range 18-93) years. The majority of pts were male (55%) and white (82%), with good PS as indicated by an ECOG 0-1 (71%). The initial skin presentation consisted of tumors in 62% of the pts, while 34% presented with plaques or patches. Notably, no pts presented with erythroderma. Most pts underwent PET scan for staging at initial diagnosis (83%) with the majority having early-stage (IA-IIA) disease (86%). Furthermore, palpable lymph nodes (11%) and the presence of B symptoms (4%) were rare at diagnosis, and no pts had blood involvement. The most common sites of involvement were extremities (33%) followed by the head and neck (H&N) and trunk (31% each). Immunophenotyping revealed CD4 positivity in 59% of pts and CD8 positivity in 25%. The T cell receptor (TCR) rearrangement was positive in 28% of pts, though it was not completed in the majority of cases (72%). Most common initial treatments included localized radiation (61%) and surgical excision (19%). A small subset of pts received frontline systemic chemotherapy regimens such as cytotoxic chemotherapy (11%), BV (8%) and oral methotrexate (MTX) (8%). Approximately 7% of the pts had a stem cell transplant. Overall response rate (ORR) for radiation, oral MTX, BV and cytotoxic chemotherapy were 78% (CR:78% 74/100), 42% (CR:63% 6/12) and 39% (CR:67% 6/12), 89% (CR: 88% 15/18) respectively. At a median follow-up of 3.8 years (range 0.04-10.23), the median RFS and OS were 2.7 years (95% CI:1.86, 3.43) and 12 years (95% CI:10.6- NA) respectively. The estimated 3- and 5-year RFS are 46% (95% CI:0.38, 0.55) and 37% (95% CI:0.28, 0.46) respectively. The estimated 3- and 5-year OS were 89% (95% CI:0.82, 0.93) and 82% (95% CI:0.73, 0.88) respectively. At the time of the last follow-up, 79% were alive, while 21% were deceased. The cause of death (COD) was unknown in 50% of the cases and only 10% (3/of deaths were attributed to lymphoma. Other known CODs included infection (20%) and second malignancies 7%. On univariate analysis (UVA), age (p=.007), female sex (p=.04), ECOG PS 1-2 compared to 0 (p=.007) and prior transplant (p=.009) predicted for worse RFS. On multivariate analysis (MVA), only ECOG PS 1-2 (HR 2.31, 95 CI:1.06, 1.18, p=.009) and prior transplant (HR 5.38, 95 CI:2.30, 12.57, p=.0001) had a significant impact on RFS. Age and presence of B symptoms were strong predictors of OS on both UVA (age p=<.0001; B symptoms p=<.0001) and MVA (age: HR 1.12, 95 CI:1.06, 1.18, p=<.0001; B symptoms: HR 16.48, 95 CI: 3.69, 73.60, p=.0002). However, the impact of B symptoms should be interpreted with caution as only 4% of pts presented with this at baseline. On UVA, each one-year increase in age was associated with an 8.5% rise in the risk of death. ECOG PS 1-2 was associated with worse OS on univariate analysis (HR 2.62, 95% CI 0.99, 6.93, p=.05), but was not significant on MVA (HR 1.05, 95% CI 0.368, 2.974, p=.93). Conclusions: In this large RWA of PCALCL, excellent long-term survival was observed with predominantly skin directed frontline therapies. The use of systemic treatments, including BV, was infrequent as first line therapy. Older age and poor PS were significant predictors for reduced survival.

Abstract Background Previous studies in aggressive B-cell lymphoma demonstrate that patients with shorter diagnosis-to-treatment intervals (DTI) represent those with higher risk disease. This suggests that patients enrolled in clinical trials may carry a selection bias as they often have longer DTI than patients in the general population. This has important implications for clinical research design and the generalizability of clinical trials in aggressive lymphomas. However, the prognostic implications of DTI have not been evaluated in peripheral T-cell lymphomas (PTCL). Therefore, we examined DTI and its association with clinical factors and outcomes in a prospective observational cohort of patients with PTCL from the United States within the LEO (Lymphoma Epidemiology and Outcomes) and MER (University of Iowa and Mayo Clinic Specialized Programs of Research Excellence Molecular Epidemiology Resource). Patients and Methods We evaluated patients enrolled to the MER (2002-2015) and LEO (2015-2020) cohorts with the following forms of PTCL: PTCL-not otherwise specified (PTCL-NOS, n=217), nodal T-follicular helper (TFH) cell lymphoma (nTFHL, n=153), anaplastic large cell lymphoma (ALCL), ALK positive (ALCL, ALK+, n=74), ALCL, ALK negative (ALCL, ALK-, n=95), enteropathy associated T-cell lymphoma (n=18), and monomorphic epitheliotropic intestinal T-cell lymphoma (n=2). Associations of DTI with clinical factors and outcomes were examined using Kaplan Meier and Cox models. Event free survival (EFS) was defined as the time from start of treatment to relapse/progression, start of 2nd line therapy, or death from any cause. Overall survival (OS) was defined as the time from start of treatment until death from any cause. DTI was defined as the number of days between the first diagnostic biopsy and the start of therapy. Patients who were initially observed or had DTI > 100 days were excluded. Results In 559 patients (229 MER and 330 LEO), median age was 60, 34% had IPI>2 and 71% were stage III/IV. 472 (84%) patients initially received anthracycline-based chemotherapy. Median DTI was 23 days (interquartile range (IQR): 12-39) and was similar in MER (21 days, IQR: 11-33) and LEO (25 days, IQR: 14-42). 168 (30%) patients had DTI 0-14 days, 178 (32%) 15-28 days, and 213 (38%) 29-100 days. Overall in the cohort, shorter DTI was associated with a worse 5-year OS (DTI 0-14 days: 43%; DTI 15-28 days: 53%; DTI 29-100 days: 58%, p<0.001) and 5-year EFS (DTI 0-14 days: 31%; DTI 15-28 days: 39%; DTI 29-100 days: 45%, p<0.001). In multivariable analyses, the association of DTI with outcomes remained consistent after adjusting for age and International Prognostic Index (IPI). Shorter DTI was strongly associated with adverse clinical factors, including elevated lactate dehydrogenase levels, poor performance status, B-symptoms, and higher IPI in both cohorts (all P < .003). DTI was not associated with age, sex, or distance from the LEO/MER center (all p>0.3). 6% patients with DTI of 0-14 days received 1L treatment on a clinical trial, compared to 11% with DTI 15-28 days and 13% with DTI 29-100 days, underscoring that patients with lower DTI may be underrepresented in clinical trials. When examining within PTCL subtypes, the association between short DTI (0-14 days) and inferior outcomes was most prominent in PTCL, NOS (OS HR=2.13, 95% CI: 1.52-2.94; EFS HR =1.49, 95% CI: 1.19-1.85). Associations between short DTI and outcomes were weaker in other subtypes: nTFHL (OS HR=1.28, 95% CI: 0.83-2.00; EFS HR =1.22, 95% CI: 0.82-1.81), ALCL, ALK-, (OS HR=1.30, 95% CI: 0.59-2.86; EFS HR =1.32, 95% CI: 0.68-2.56), ALCL, ALK+, (OS HR=1.05, 95% CI: 0.26-4.17; EFS HR =2.12, 95% CI: 0.84-5.26). Conclusion Shorter DTI is associated adverse prognostic clinical factors (LDH, stage, high IPI) and inferior EFS and OS in newly diagnosed PTCL. Patients with DTI ≤ 14 days, which represents approximately 1/3 patients with PTCL, may be underrepresented in clinical trials. Understanding of this selection bias should inform clinical trial design and interpretation. Future studies should consider strategies to minimize barriers to enrollment for patients with low DTI.

Abstract Myeloproliferative neoplasms (MPNs) are typically ascribed to hyperactive JAK-STAT signaling via mutations in JAK2, CALR, or MPL. Here, we characterize how activating mutations in the calcium sensor STIM1, previously established as the cause of Stormorken Syndrome (SS), a rare congenital disorder, are sufficient to drive development of myelofibrosis (MF). We further uncover distinct interactions between STIM1 activity and JAK2 versus CALR driven MPNs. We initially identified two SS patients with activating mutations in STIM1 (R304W and S88G) and features of MF, including marked reticulin fibrosis with megakaryocytic hyperplasia and atypia. This led us to hypothesize that altered calcium signaling may play a role in the development of MF in both SS and MPNs. Single cell RNA sequencing performed on samples from both patients demonstrated elevated NFκB inflammatory signaling in monocyte populations, suggesting a link between altered STIM1 and store operated calcium entry (SOCE) activity and aberrant inflammation, thereby contributing to MF development. To corroborate these findings from our SS patients, we generated a knock-in mouse model of the heterozygous R304W mutation. Induction of hematopoietic-specific expression of mutant Stim1 with Vav-Cre recapitulated the hematological features of SS, including elevated SOCE activity and thrombocytopenia. We also recapitulated MF features including the development of bone marrow fibrosis and severe osteosclerosis, with the mice developing splenomegaly as young as 9 weeks old. In ex vivo megakaryocyte differentiation assays with our Stim1 R304W knock-in mice, we also observed aberrant cytoskeletal organization and elevated TGFβ mRNA expression. When induction was driven universally through CMV-Cre, we also validated that mice recapitulated multiple SS features, including thrombocytopenia, tubular aggregate myopathy, growth deficiency, and the development of bone marrow fibrosis as young as 10 weeks. We additionally identified a separate cohort of 9 related individuals with SS and STIM1 mutations (L92V) as well as a separate patient with the R304W mutation. In ex vivo megakaryocytic differentiation assays, cells from SS patients demonstrated defective thrombopoiesis with significantly decreased proplatelet formation, and displayed aberrant cytoskeletal formation within the pro-platelet termini, in conjunction with increased expression of TGFβ. Further supporting a role for STIM1 in MPNs, we identified upregulation of STIM1 expression in MPN patient CD34+ hematopoietic stem/progenitors' cells (HSPCs), we well as megakaryocyte progenitors and platelets, including those with CALR or JAK2 mutations. To evaluate the functional role of STIM1 in MPNs, we generated patient-derived xenograft (PDX) models with CALR and JAK2-mutantpatient samples subjected to CRISPR ablation of STIM1. In an initial CALR-mutant PDX experiment, abrogation of STIM1 led to decreased human CD45+ cell engraftment in conjunction with prolonged survival. In a second CALR-mutant PDX experiment, STIM1 targeting did not overtly impact engraftment or survival. In contrast, CRISPR ablation of STIM1 in JAK2-mutant PDX models led to exacerbated disease phenotypes, including increased human CD45+ cell engraftment, increased splenomegaly, and early lethality. Altogether, this study represents the first demonstration of MF development in patients with Stormorken Syndrome and reveals a previously unrecognized role of aberrant SOCE underlying SS and MPNs. We recapitulated these findings in a novel conditional mouse model. These findings also illustrate unique interactions between STIM1 and JAK2 and CALR driven MPNs. These observations have important implications for the development of targeted therapeutic approaches for these disorders.

Abstract INTRODUCTION Bispecific antibodies (BsAbs) have emerged as transformative therapies for hematologic malignancies, with several agents now approved for relapsed/refractory acute lymphoblastic leukemia (ALL), multiple myeloma (MM), and non-Hodgkin lymphoma (NHL). These therapies have demonstrated remarkable overall response rates across multiple clinical trials, with some now being evaluated in frontline settings. Recent publications have raised concerns about SPMs following CAR-T cell therapy, with the FDA requiring boxed warnings after reports indicated SPMs rates of up to 5%. However, the incidence of SPMs with BsAbs remains poorly characterized, despite shared mechanisms of T-cell activation. METHODS We conducted a systematic literature search via PubMed to identify peer-reviewed publications reporting clinical trials of FDA-approved BsAbs for hematological malignancies. Included agents were blinatumomab (CD19×CD3), glofitamab, mosunetuzumab, epcoritamab, and odronextamab (all CD20×CD3), as well as elranatamab, teclistamab, and linvoseltamab (BCMA×CD3), and talquetamab (GPRC5DxCD3). Eligible studies included phase I-III trials evaluating BsAbs either as monotherapy or combination therapy, irrespective of prior lines of treatment. Studies published only as abstracts were excluded due to insufficient adverse event reporting. Trials were screened for documentation of SPMs, both from main and supplemental publications. Trials were categorized based on SPMs reporting: “N/A” (insufficient data), “No” (explicit acknowledgment of no SPMs or comprehensive AEs reports with no malignancy entries), and “Yes” (direct reporting of SPMs). Only patients who received BsAbs were included in pooled analyses; comparator or control arms from randomized trials were excluded. For trials reporting patient numbers, median follow-up and SPM counts, we calculated crude incidence rates and cumulative incidence per 100 person-years using estimated total person-years. RESULTS We identified 19 clinical trials encompassing 5,133 patients across ALL (n=5 trials), MM (n=4), and NHL (n=10, including DLBCL and follicular lymphoma). Phase distribution included 5 phase 3 trials and 14 phase 1/2 trials. Most trials (n=16, 84%) evaluated BsAbs as monotherapy. The median number of patients enrolled per trial was 145 (range 54-718; mean 193), with a median follow-up of 14.3 months (range 4.2-43 months; mean 18.3). Four trials (21%) had insufficient adverse event data and were excluded from the analysis. The final pooled cohort analysis included 3,215 patients with available long-term safety data and a cumulative follow-up of 6,270 person-years. Across this cohort, 5 SPMs were reported, corresponding to a crude incidence of 0.16% and a cumulative incidence rate of 0.08 per 100-person years. These included 3 cases reported under “neoplasms benign, malignant and unspecified” in the TOWER trial (1 extramedullary leukemic infiltration, 1 pulmonary leukemic infiltration and 1 acute lymphocytic leukemia), along with 1 lung malignancy and 1 case of Hodgkin's lymphoma both from mosunetuzumab studies. CONCLUSION This analysis suggests a low incidence of SPMs with BsAb therapy compared to CAR-T therapy and appears consistent with expected baseline rates in heavily pretreated hematologic malignancy populations. Notably, some reported cases may represent disease progression rather than true SPMs. However, limited follow-up duration across trials warrants continued long-term surveillance, particularly as agents move to frontline settings where longer survival may reveal delayed malignancies.

Abstract Introduction: Epcoritamab (epcor) was the first CD3xCD20 bispecific antibody approved for treatment of R/R DLBCL in May 2023 based on its efficacy and safety in EPCORE NHL-1. Patients (pts) enrolled in clinical trials are highly selected, and those with high-risk features, such as primary refractory disease, early post-CAR T relapse, poor Eastern Cooperative Oncology Group (ECOG) performance status (PS), and CD20+ status are often underrepresented or excluded. As epcor use expands in more heterogeneous, real-world populations, there is increasing interest in understanding pt characteristics and response outcomes associated with its use outside of clinical trials. In particular, pts with DLBCL that is resistant to, or relapse soon after, CAR T are left with limited treatment options and often present with rapidly progressive, resistant disease, making them especially challenging to manage. Generating real-world evidence is critical for informing optimal use of epcor in routine practice. Methods: Real-EPCOR is a multicenter US retrospective chart review study at >8 academic and community oncology centers designed to evaluate the real-world use of epcor. Eligible pts are adults (≥18 years) with R/R DLBCL and ≥2 prior lines of therapy (LOT) who initiated epcor outside of a clinical trial after 5/19/23. Pt demographic, clinical, and treatment data were collected, including ECOG PS, refractory status, prior CAR T, and CD20+ status. Overall response rate (ORR) was evaluated during epcor treatment and defined as the proportion of pts achieving complete response (CR) or partial response among pts with ≥1 evaluable response assessment or who died due to disease progression before response assessment. ORR and CR rate were calculated for the entire cohort, for pts receiving ≥2 cycles of epcor (full cycle is 28 days), and for pts who received prior CAR T. Results: This interim analysis included 34 pts from 2 centers. Data collection and analysis is ongoing and updated results with additional pts and longer follow-up may be included at time of presentation. Median age was 67 years; 68% pts were male and 85% were White. Median time from DLBCL diagnosis to initiation of epcor was 15.5 months. The most common comorbidities were cardiovascular disease (59%) and diabetes mellitus (29%). ECOG PS was ≥2 in 29% of pts, and 85% of pts had Ann Arbor stage 3-4 disease. Nearly all (97%) had CD20+ DLBCL. High-risk features were common at time of epcor initiation, including 53% with International Prognostic Index (IPI) ≥3, 26% with double-hit, and 24% with non-GCB subtype. Among pts who received ≥2 cycles of epcor (n=15), 20% had ECOG PS ≥2 and 33% had IPI ≥3; in post-CAR T pts, 22% had ECOG PS ≥2 and 57% had IPI ≥3. Median number of prior LOT was 3 (range: 2–9); 44% of pts initiated epcor as 3L therapy. Prior to epcor, 41% had primary refractory disease. Following their most recent therapy, 72% had refractory disease, and 43% had DLBCL that was refractory to all prior LOT in those with known refractory status. Most pts (68%) received prior CAR T, with a median interval of 4.6 months from infusion to epcor initiation, and 23% initiated epcor ≤2 months from CAR T. 15 pts (44%) received CAR T in the LOT immediately prior to epcor, 9 (60%) of whom were refractory to CAR T. The ORR was 50% and CR rate was 29% in the overall evaluable population (n=24). 10 pts were not evaluable, as they did not undergo a response assessment either because they remained alive without assessment or experienced a non-progression-related event. Among pts who received ≥2 cycles of epcor, ORR was 85% and CR rate was 54% in the evaluable population (n=13). Among 23 post-CAR T pts, ORR was 53% and CR rate was 33% in the evaluable population (n=15). Conclusion: In this real-world interim analysis, pts with R/R DLBCL treated with epcor had a high proportion of CD20+ disease, higher-risk clinical features, greater comorbidity burden, and more complex treatment histories, including a substantial proportion with prior CAR T, compared to pts in EPCORE NHL-1. Therefore, the ORR remains highly meaningful in the overall cohort despite being lower than the trial. Encouraging ORRs among those who received ≥2 cycles of epcor or had prior CAR T suggest that epcor monotherapy may provide clinical benefit even in difficult-to-treat pts in the real-world setting. Ongoing real-world survival analyses will inform the optimal use of epcor within the evolving treatment landscape of R/R DLBCL.

Abstract Background: Luspatercept, an erythroid maturation agent, has shown efficacy in improving anemia in both β-thalassemia and lower-risk myelodysplastic syndromes (MDS). In the BELIEVE trial, which led to its approval in transfusion-dependent β-thalassemia, thromboembolic events were notably higher in patients with risk factors such as splenectomy. More recently, the COMMANDS trial demonstrated superior transfusion independence with luspatercept over erythropoiesis-stimulating agents (ESAs) in ESA-naive, lower-risk MDS patients. However, limited data exist regarding comparative thrombotic risk in real-world MDS populations. We conducted a multicenter, real-world study to evaluate thrombotic event rates associated with luspatercept versus ESAs in MDS patients without prior venous thromboembolism (VTE). Methods: We queried the TriNetX Research Network, a federated real-time electronic health record (EHR) database covering over 100 million patients across major healthcare organizations. Adults (≥18 years) with a diagnosis of MDS (ICD-10-CM code D46) and no prior history of deep vein thrombosis (DVT) or pulmonary embolism (PE) were included. Patients were stratified based on treatment with luspatercept or ESAs (epoetin alfa or darbepoetin alfa). Propensity score matching (PSM) using a 1:1 nearest-neighbor algorithm without replacement was performed to balance demographics and clinical covariates. Primary outcomes included the incidence of DVT, PE, and composite VTE events within 12 months of therapy initiation. Results: A total of 6,448 patients with MDS and no prior VTE were identified: 5,698 received ESAs and 750 received luspatercept. The overall mean age was 72.5 ± 13.5 years, with 48.1% male. After PSM, 741 patients were included in each treatment arm. The matched cohort had a mean age of 76.7 ± 10.7 years, and 41.3% were female. In the ESA group, 58/741 (7.8%) developed DVT compared to 27/741 (3.6%) in the luspatercept group (Hazard Ratio [HR] 1.4; 95% CI, 0.9–2.3). PE occurred in 27 ESA-treated patients (3.6%) versus 13 luspatercept-treated patients (1.8%) (HR 1.3; 95% CI, 0.6–2.7; p=0.941). The overall composite VTE rate was 10.0% (74/741) in the ESA group and 4.9% (36/741) in the luspatercept group (HR 1.3; 95% CI, 0.9–2.0; p=0.732). Conclusion: In this large, multicenter real-world analysis, we observed a numerically lower incidence of thrombotic events with luspatercept compared to erythropoietin-based agents in patients with MDS, though differences did not reach statistical significance. These findings support the thrombotic safety profile of luspatercept observed in clinical trials and warrant further prospective validation.

Abstract Introduction: Somatic mutations in UBA1, encoding an E1 ubiquitin activating enzyme, have recently been linked to an adult-onset, severe inflammation syndrome called VEXAS (Vacuoles, E1-enzyme, X-linked, Autoinflammatory, Somatic). VEXAS is characterized by systemic inflammation and hematologic abnormalities. While the majority of identified mutations in UBA1 are located in exonic regions, the role of non-coding and intronic mutations in the pathogenesis of VEXAS remains largely unexplored. In this study, we investigated the potential contribution of intronic mutations to VEXAS pathogenesis. Methods: To investigate mutations affecting UBA1 outside the region typically covered in targeted panels (exon 3), whole exome (WES) and genome sequencing (WGS) was performed on peripheral blood of patients with VEXAS-associated clinical presentation previously negative for UBA1 mutations per clinical testing. 265 patients were profiled by WES (~100X) and 36 patients were profiled by WGS (~55X). Clinical history was reviewed for these patients for VEXAS-associated presentation including a combination of hematologic and rheumatologic disease in adults. Participants with known pathogenic or likely pathogenic (P/LP) variants in UBA1 or other genetic causes of systemic autoinflammatory disease were excluded. UBA1 transcript and protein expression were assessed by PCR and western blot, respectively, in one case where peripheral blood mononuclear cells were available. Results: We identified 7 patients with VEXAS-like presentation with intronic single nucleotide variants or deletions. Five patients had a recurrent point mutation (median VAF: 0.78; range: 0.38-0.97). 5 patients had been diagnosed with MDS, and bone marrow biopsy revealed vacuolated progenitor cells in 3 patients. The most frequent clinical manifestations included skin rash (n=6), joint pain (n=4), vasculitis (n=4), and chondritis (n=2). One patient had been diagnosed with acute myeloid leukemia with myelodysplasia related changes, with co-mutations in IDH1 and SRSF2. Two additional patients had mutations in ASXL1 of which one also had a ZRSR2 mutation. No co-occurring myeloid driver gene mutations were found in the other cases. Noncoding mutations, similar to canonical UBA1 disease causing mutations, were shown to be lineage restricted to myeloid cells. To assess the functional impact of mutations, CD14+ monocytes were isolated from the peripheral blood. Compared to the CD14- fraction, the CD14+ fraction revealed a decrease in the UBA1 transcript as well as UBA1 protein level. One patient demonstrated loss of novel UBA1 mutation after hypomethylating agent treatment, and allogeneic transplant, placing the patient in remission.Conclusions:Our findings of intronic and non-coding UBA1 mutations in patients with VEXAS-associated clinical presentation suggests these variants may affect the regulation of UBA1 transcription, representing a potential new mechanism of pathogenesis. Further functional studies are underway to understand how these variants contribute to impaired UBA1 activity and VEXAS disease pathogenesis. Collectively, our results advocate for a broader approach in genetic testing for UBA1 mutations and pave the way for improved diagnostic and therapeutic strategies for VEXAS syndrome.

Abstract Introduction:A comprehensive integration of significantly mutated genes and pathways with molecular subgroups is lacking in adult B-ALL. Furthermore, the genomic drivers underlying each subgroup remain to be identified.We aimed to perform genomic analysis on a large cohort of patients with adult B-ALL, and to correlate genomic markers with achievement of MRD negativity enabling blinatumomab randomization, and with subsequent response to blinatumomab. Methods:For genomic analysis, we studied 569 adults with newly diagnosed B-ALL registered for initial screening on the ECOG-ACRIN-led E1910 trial (NCT02003222), which evaluated the addition of blinatumomab to standard consolidation chemotherapy. The median age was 52 yrs (range 30 to 71 yrs), with 52% males. Analysis was performed on tumor and matched-normal samples using whole transcriptome sequencing (RNA-seq; tumor only; n=569), whole exome sequencing (n=490), whole genome sequencing (n=131), and single nucleotide polymorphism array (n=445). B-ALL cases were classified into 22 molecular groups. Outcome analysis was limited to patients enrolled and treated on E1910 (n=319). Results: Driver genes (n=268) were identified by the mutation-significance detection tool dNdScv or by the presence of pathogenic variants in known cancer genes, with NUP188 identified as a novel driver gene. Recurrently mutated pathways included: B-cell development (46%), cell cycle (44%), epigenetic regulation (30%), other transcriptional regulation (27%), Ras signaling (25%), RNA machinery (17%) and JAK-STAT signaling (8%). A high frequency of high-risk subtypes was observed including BCR::ABL1 (20%), BCR::ABL1-like (18%), low hypodiploid (14%) and KMT2A (12%). Using tSNE analysis, we identified a new cluster of cases (n=20, 3.5%) lacking a known subgroup driver, with overexpression of CEBPA (n=13) or CEBPB (n=7), distinct from CEBPE/ZEB2, termed “CEBP-altered” ALL (CEBPalt). Five of 13 cases with high CEBPA expression harbored an IGH::CEBPA rearrangement and one harbored a RXRA::CEBPA enhancer hijacking alteration. Of the 7 cases with high CEBPB expression, 5 harbored IGH::CEBPB, and two of these had concomitant clonal BCR::ABL1 fusions. To identify additional mechanisms of CEBP deregulation, in situ Hi-C coupled to H3K27 acetylation immunoprecipitation (HiChIP) was performed on 5 cases. Four cases showed evidence of de novo CEBPA enhancer activity. In two cases, we identified novel insertions (12 and 34nt) ~2kb downstream of CEBPA. A novel translocation and enhancer hijacking event between LINC00426 and the 5' UTR of CEBPB was identified in the remaining case. Overall, we confirmed genomic alterations of CEBPA or CEBPB in 16 of 20 cases with available material. Thus, we have identified a new molecular subgroup of adult B-ALL characterized by genomic alterations that drive enhancer hijacking and oncogenic deregulation of CEBPA/CEBPB. Several subgroups were enriched in patients that failed induction chemotherapy (n=62) or were MRD-positive (n=63) compared to those that achieved MRD-negative status (n=194): BCR::ABL1-like (30 vs 14%, p<0.001), KMT2A (18 vs 9%, p=0.03) and BCL2/MYC (5 vs 1%, p=0.06). Conversely, the following subgroups were enriched in patients that achieved MRD-negativity: PAX5alt (6 vs 18%, p=0.002), TCF3::PBX1 (0 vs 5%, p=0.01) and ZNF384 (2 vs 6%, p=0.08) Within each molecular subgroup we compared the survival of patients who achieved MRD-negative status after induction and were randomized to receive blinatumomab plus chemotherapy (n=93) or chemotherapy only (n=91). Although numbers were low, blinatumomab improved relapse-free survival for patients with hyperdiploid, PAX5alt, BCR::ABL1-like and KMT2A ALL compared to chemotherapy alone. Clonal hematopoiesis of indeterminate potential (CHIP)-related gene mutations were identified in 121 of 417 cases analyzed (29% total: somatic 74%, remission 31%, both 5%). TP53 mutations were most frequent (n=65 patients), with the majority identified in patients with low hypodiploid (n=52). Interestingly, patients with CRLF2 rearrangements collectively harbored the highest number of other CHIP gene mutations (n=13), including DNMT3A (n=4), TET2 (n=3) and ASXL1 (n=3). Conclusions:We provide a comprehensive landscape of genomic alterations in adult B-ALL and identify a new group characterized by deregulation of CEBPA/CEBPB (CEBPalt). We also provide insights into the efficacy of blinatumomab in different molecular subgroups of adult B-ALL.

Abstract Introduction Hispanic and non-Hispanic Black (NHB) patients have worse HCT survival compared to non-Hispanic White (NHW) patients and were less likely to utilize an unrelated HCT donor (Khera et al. Blood Adv. 2024; Hahn et al. JAMA Netw Open. 2024), but this difference has not been evaluated in the PTCy era. PTCy reduces graft-versus-host disease (GvHD) and allows for increased availability of allogeneic donors in minority patients. It is important to know the best donor source for each ethnicity. In this study, we investigated the association of race/ethnicity and donor type on overall survival (OS). Methods We performed a secondary analysis of adult patients (>19 yrs) who were selected if they had a peripheral blood allogeneic HCT from 2013-2018 and received PTCy for GVHD prophylaxis using a publicly available dataset from the Center for International Blood and Marrow Transplantation Research Program. Kaplan-Meier curves estimated 2-year OS, and differences were compared using log-rank tests. X2 tests helped identify potential confounders. Analyses were stratified by donor type and self-reported race/ethnicity. The Cox Proportional Hazards model evaluated 2-year OS using a backwards elimination method to build the final prediction model. P<0.05 was considered statistically significant. Results Of 4,031 patients included, 70% were NHW, 16% were NHB, and 13% were Hispanic. The most common donor was Haploidentical (Haplo; 64%), followed by matched unrelated donor (MUD; 19%), matched related donor (MRD; 10%), and mismatched unrelated donor 7%). Hispanic patients were younger than NHW and NHB (P<0.0001) and more were transplanted in CR (P<0.0001). Additionally, most Hispanic and NHB patients received a Haplo HCT (77 and 83%, respectively). NHW patients also received Haplo HCTs (57%) as well as MUD HCTs (24%). Most patients had acute myeloid leukemia (40%) followed by myelodysplastic syndrome (22%) and received reduced intensity conditioning (58%). MUD patients who received PTCy had the highest 2-year OS compared to other donors (65 vs 58-61%; P=0.03). Higher OS was observed in younger patients (20-39 yrs: 69% vs 60+ yrs: 53%; P<0.001) and patients with non-malignant diseases (80%) or Hodgkin lymphoma (79%) compared to patients with plasma cell (52%) and myelodysplastic disorders (55%; P<0.0001). For NHW patients, patients transplanted with a MUD had higher OS than other donor types (67 vs 58-60%; p=0.0006). In contrast, NHB transplanted with MRD, Haplo, or MMUD had the highest OS compared to MUD, although this was not statistically significant (61-66% vs 42%; p=0.4). Hispanic patients transplanted with a related donor (MRD and Haplo) had higher OS compared to patients who had an unrelated donor (MUD and MMUD; 66-67 vs 48-58%; P=0.1). Within each donor source, we tested for a racial disparity in OS. There was no difference in OS by race/ethnicity in MRD or MMUD HCTs. In Haplo HCTs, Hispanic patients had the highest OS followed by NHB and then NHW (66, 61, vs 58%; P=0.005). In MUD HCTs, NHW patients had higher OS than Hispanic or NHB patients (67, 48, vs 42%; P=0.02). Significant factors associated with OS in multivariable analyses included donor type, age, disease, year of transplant, conditioning intensity, Karnofsky Performance Score, donor/recipient CMV serostatus, and disease risk index. Results were stratified by race/ethnicity. For NHW patients, mortality risk was higher for HCT patients receiving a MRD, Haplo, or MMUD compared to a MUD (HR=1.25-1.39; P=0.001). In contrast, NHB patients receiving a MUD had a higher risk of mortality compared to a Haplo, MRD, or MMUD (HR=1.67; P=0.06). In Hispanic patients, MUDs and MMUDs had a higher mortality risk than MRD or Haplo HCT (HR=1.48; P=0.07). Conclusion OS differed by race/ethnicity and donor type. Our findings should be validated by expanding the analysis to include patients treated with PTCy after the publication of BMT CTN 1703 results (Bolaños-Mead et al. NEJM. 2023). When selecting donors for HCT patients, consideration should be given to patient race/ethnicity.

Abstract Background: VEXAS (Vacuoles, E1 enzyme, X-linked, Autoinflammatory, Somatic) syndrome is a hemato-inflammatory syndrome due to somatic mutations in UBA1 gene. Recently, DNA methyltransferase inhibitors (specifically, 5-azacitidine) and allogeneic hematopoietic stem cell transplantation (alloHSCT) have shown success in eradication of UBA1 clones and clinical remission in some patients. This study aims to provide a comparative efficacy analysis between DNA methyltransferase inhibitors (hypomethylating agents/HMA) versus alloHSCT in VEXAS syndrome patients. Methods: This is a multi-center, retrospective cohort study. UBA1 mutations were detected either through next generation sequencing [NGS, limit of detection (LOD) 2% variant allele fraction (VAF)] or quantitative droplet digital polymerase chain reaction testing (ddPCR, LOD 0.5% VAF). Outcomes of interest included overall survival (OS), glucocorticoid (GC) discontinuation/reduction in dose (prednisone < 10 mg/day), and complete molecular remission (CMR, defined as an undetectable UBA1 mutation). OS was calculated from the time of diagnosis to death or last follow up. Cumulative incidence of reduction in GC dose was calculated using competing risk analysis after accounting for death. Results: Between years 2020-2024, a total of thirty-nine male patients (median age 67, range 45-82 years) with VEXAS syndrome, necessity for therapy (GC-refractory inflammation and/or progressive marrow failure/myeloid neoplasm) and confirmed UBA1 pathogenic mutation were included. Of these, 18 (46%) received HMA therapy (5-azacitidine 72% and Decitabine 28%) with a median of 4 (range 1-36) cycles. and 21 (54%) underwent alloHSCT (MSD=4, MUD=12, MMUD=2, and haploidentical=3), all received reduced intensity conditioning (Flu/Mel =11, Flu/Bu=5, Flu/Cy/TBI=2, and TBF=3) and 91% received post-transplant cyclophosphamide-based graft-versus-host disease (GVHD) prophylaxis (only 2 patients in alloHSCT group received prior HMA without benefit). Baseline characteristics were well-balanced between HMA and alloHSCT groups; age at treatment (median 70 vs 65 years, p=0.2), and UBA1 M41V subtype (25% vs 40%, p=0.3), cytogenetic and non-UBA1 mutation abnormalities (p=0.4), prior lines of therapy (median 4 in both, p=0.5), time from diagnosis to therapy (median 7 vs 13 months, p=0.15), indication for therapy (p=0.12), Charlson CI scores (median 4 in both, p=0.4) and HCI-CI scores (median 4 in both, p=0.7). At a median follow-up of 45 (range 7-57) months, 11 (28%) deaths (alloHSCT=3 and HMA=8) were documented. Causes of death included infections (n=6), cardiac disease (n=2), poor graft function (n=2) and pulmonary GVHD (n=1). Compared to HMA therapy, alloHSCT group demonstrated higher rates of GC discontinuation (52% vs 6%, p<0.01) and CMR (evaluable= 22, 100% vs 50%, p<0.01). In the HMA group, 50% (n=9) discontinued therapy after a median of 4 months due to infectious complications or lack of benefit. In the alloHSCT group, 3 (14%) patients developed grade 2 acute GVHD (1-skin, 2-gut, no grade 3-4 acute GVHD) and 4 (19%) experienced moderate to severe chronic GvHD (2-lung, 2-mucocutaneous). In multivariable analysis (MVA) adjusted for age and HCT-CI, alloHSCT was identified as the strongest favorable predictor for OS (HR 0.18 95% CI 0.04-0.8) with similar results when analysis was restricted to transplant-eligible patients < 75 years of age (HR 0.1, 95% CI 0.03-0.6). In a 6-month post-treatment landmark analysis (n=31 evaluable), patients who underwent alloHSCT (n=17) exhibited numerically superior GC discontiuation rate (29% vs 14%, p=0.049) and subsequent OS compared to HMA (2-years OS: 84% vs. 61%, median not reached vs 25 months, 95% CI: 0.06–1.7). In a post-treatment competing risk [GC dose reduction (death)] analysis alloHSCT was associated with superior 2-, and 3-year rates of 57% (10%), and 76% (10%), compared to HMA 22% (24%), and 31% (42%) [p<0.01 (0.04)]. AlloHSCT was also associated with higher rate of CMR (evaluable= 21, alloHSCT N=16 and HMA N=5, 100% vs 60%, p=0.01). At the last follow up, none of the patients who achieved CMR had re-emergence of the UBA1 clone (despite early mixed chimerism). Conclusions: This study represents the largest comparative analysis of alloHSCT versus HMA therapy in VEXAS syndrome, and confirms superiority of alloHSCT in achieving molecular remission, GC discontinuation/dose reduction, and overall survival. Prospective clinical trial confirmation is warranted.