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BACKGROUND AND OBJECTIVES: Stereotactic radiosurgery (SRS) for brain arteriovenous malformations (AVMs) can cause radiation-induced changes (RIC), but its interactions with AVM embolization are not well established. The aim of this study was to assess the effect of previous embolization on RIC in SRS-treated AVM patients. METHODS: Data of AVM patients treated with single-session SRS from 1987 to 2018 were retrieved from the International Radiosurgery Research Foundation. Univariable and stepwise backward logistic regression models were used to identify RIC predictors. Patients were stratified into those who received pre-SRS embolization (E + SRS) vs those who did not (SRS-only). Radiologic RIC (rRIC) was the primary end point. Secondary outcomes included symptomatic RIC (sRIC) and permanent symptomatic RIC (pRIC). RESULTS: Among 1187 AVM patients, the mean age was 36.4 years (SD 16.8), with 50.4% female patients. AVMs had a mean untreated AVM volume of 5.2 cm 3 . A total of 130 patients (11%) underwent neoadjuvant embolization (E + SRS). The overall rRIC and sRIC rates were 32.8% and 12.1%, respectively, with time to rRIC and sRIC being significantly longer in the E + SRS vs SRS-only cohorts (103.6 ± 339.4 vs 11.3 ± 12.5 and 60.4 ± 262.9 vs 9.5 ± 9.0 months, respectively). Seizures at presentation and ≥3-cm untreated AVM volume significantly correlated with a higher likelihood of rRIC (adjusted odds ratio [aOR] 2.32 [1.25-4.30] and aOR 2.77 [1.24-6.16], respectively). Age and pre-SRS embolization were associated with a significantly lower risk of rRIC (aOR 0.97 [0.96-0.99] and aOR 0.32 [0.13-0.74], respectively). The E + SRS cohort had significantly reduced odds of rRIC (aOR = 0.37 [0.15-0.89]) and pRIC (aOR = 0.04 [0.00-0.30]) after adjusting for significant covariates. CONCLUSION: Seizures at presentation and larger untreated AVM volume were independently associated with an increased risk of rRIC, whereas older age and pre-SRS embolization were protective. Notably, patients who underwent embolization before SRS had lower odds of rRIC and pRIC, with delayed onset of complications compared with SRS-only.

Objective Antiphospholipid syndrome (APS) is a thromboinflammatory disorder characterized by clinical and mechanistic heterogeneity that complicates early diagnosis and hinders targeted treatment. We aimed to identify distinct molecular endotypes among antiphospholipid antibody (aPL)–positive patients using whole‐blood transcriptomics. Methods Whole‐blood RNA sequencing was performed on 174 aPL‐positive patients, including those with primary APS (n = 102), secondary APS (n = 29), and aPL positivity without classifiable APS (n = 43). Unsupervised machine learning and immune cell deconvolution defined transcriptomic clusters and immune landscapes. Results Four transcriptionally distinct clusters were identified. At one end of the spectrum, cluster 1 showed up‐regulation of ribosomal and metabolic pathways and down‐regulation of mechanistic target of rapamycin (mTOR), NETosis, and Hippo/interleukin‐6 (IL‐6) signaling. In contrast, cluster 4 exhibited the opposite pattern, with strong up‐regulation of mTOR, NETosis, and Hippo/IL‐6 signaling. Cluster 2 demonstrated modest enrichment in messenger RNA processing and amino acid metabolism, and cluster 3 showed biosynthetic suppression with mild Hippo/IL‐6 activation. Clinically, cluster 4 stood out with higher IgG anticardiolipin and anti–β 2 ‐glycoprotein I positivity, elevated neutrophil counts, and increased urine protein‐to‐creatinine ratios. Immune deconvolution revealed distinct cell type profiles: cluster 1 was lymphoid predominant; cluster 2 had a balanced composition; cluster 3 was enriched in Treg cells, natural killer cells, macrophages, mast cells, and memory B cells; and cluster 4 was dominated by myeloid cells, including neutrophils, eosinophils, and dendritic cells. Distinct immune pathway activations were linked to clinical features, including white matter lesions, seizures, and cardiac valve disease. Conclusion This study reveals four endotypes of aPL‐positive patients, a step toward personalized medicine for APS through pathway‐informed stratification and therapy.

PURPOSE Venetoclax, an oral BCL-2 inhibitor, has efficacy in t(11;14)-positive relapsed/refractory multiple myeloma (RRMM), which is enhanced by dexamethasone, which promotes BCL-2 dependency. METHODS The randomized, open-label, phase III CANOVA study (ClinicalTrials.gov identifier: NCT03539744 ) enrolled adults with t(11;14)-positive RRMM who had received ≥2 previous lines of therapy. Patients were randomly assigned (1:1) to venetoclax-dexamethasone or pomalidomide-dexamethasone until progression or intolerable toxicity. The primary end point was independent review committee assessed–progression-free survival (PFS) in the intention-to-treat population analyzed by stratified log-rank test (two-sided type I error rate, α = .05), with hazard ratio (HR) and 95% CI estimated by stratified Cox proportional hazard model. Secondary end points included response rates, overall survival (OS), minimal residual disease (MRD) negativity rate (<10 –5 ), and safety. RESULTS Overall, 263 patients were randomly assigned (venetoclax-dexamethasone, n = 133; pomalidomide-dexamethasone, n = 130). Median PFS was 9.9 months (95% CI, 6.9 to 12.6) with venetoclax-dexamethasone versus 5.8 months (95% CI, 3.8 to 9.2) with pomalidomide-dexamethasone (HR, 0.823 [95% CI, 0.596 to 1.136]; P = .24). Overall response and very good partial response or better rates were 62% and 39%, respectively, with venetoclax-dexamethasone versus 35% and 14% with pomalidomide-dexamethasone. MRD negativity rate was 8% with venetoclax-dexamethasone and 0% with pomalidomide-dexamethasone. Median OS was 32.4 months (95% CI, 26.4 to 40.7) with venetoclax-dexamethasone and 26.9 months (95% CI, 20.4 to 38.9) with pomalidomide-dexamethasone (HR, 0.856 [95% CI, 0.612 to 1.197]). Grade ≥3 treatment-emergent adverse event rates were 67% with venetoclax-dexamethasone versus 83% with pomalidomide-dexamethasone. There were 16 (12%) treatment-emergent deaths with venetoclax-dexamethasone versus 8 (6%) with pomalidomide-dexamethasone. CONCLUSION The primary end point of PFS was not met. PFS and OS were numerically longer with venetoclax-dexamethasone versus pomalidomide-dexamethasone in t(11;14)-positive RRMM. Consistent with previous studies, infections were associated with venetoclax-dexamethasone; no new safety signals were observed.

Abstract Introduction Down-sized inflatable penile prosthesis (IPP) cylinders are useful in cases with substantial penile fibrosis such as history of priapism or prior infection. Although down-sized IPP cylinders have a clear role in fibrotic corpora, their role in primary implant cases is unclear. Objective To identify factors associated with the use of down-sized cylinders in men undergoing primary IPP placement. Methods We conducted a retrospective analysis of 4,389 patients undergoing primary IPP placement from our multicenter database. Patients were categorized by down-sized (AMS 700 CXR, Coloplast NB) vs. standard sized cylinders (AMS 700 CX, AMS 700 LGX, Coloplast Titan). We collected demographic, intraoperative, and postoperative data. A multivariable analysis was performed to identify factors associated with use of down-sized cylinders Results A total of 4,389 men undergoing primary inflatable penile prosthesis (IPP) placement were included in the study, with a mean age of 62.3 ± 10.3 years. Among them, 1,485 (34%) had diabetes and 2,131 (49%) had hypertension. A total of 406 down-sized cylinders and 3,983 standard cylinders were implanted. Non-infectious complications occurred more frequently with the use of down-sized cylinders (odds ratio [OR] = 2.0, p &lt; 0.001). Specifically, non-infectious complications were reported in 44 out of 185 men (23.8%) with down-sized cylinders, compared to 192 out of 2,727 men (10.9%) with standard cylinders. Cylinder complications constituted 13.9% and 13.0% of the non-infectious complications in the down-sized and standard cylinder groups, respectively. Conclusions The rate of cylinder-related complications were similar between the down-sized cylinder and standard cylinder groups. Urologists should be prepared to place down-sized cylinders during IPP placement in diabetic men and in men requiring serial dilation due to fibrosis. Disclosure Any of the authors act as a consultant, employee or shareholder of an industry for: Intuitive Surgical, Fidelis, Urofill, Boston Scientific, Coloplast, Cynosure, Antares Pharma, Clarus Pharmaceuticals, Acerus Pharma; Endo Pharma.

INTRODUCTION: Colorectal cancer remains a leading cause of cancer associated death in the United States and colonoscopy the primary screening strategy for prevention. Rates of adenomatous and serrated neoplasia detection are inversely associated with postcolonoscopy colorectal cancer. This crucial quality metric depends on accurate ascertainment of colorectal neoplasia findings from both endoscopy and histopathology records. We aimed to assess the feasibility of a random forest machine learning model to rapidly and accurately categorize colorectal neoplasia from electronic health record data. METHODS: A retrospective cohort study compared neoplasia detection rates among individuals undergoing colonoscopy at a large academic institution to develop a rule-based algorithm to categorize colorectal neoplasia from endoscopy reports and pathology systematized nomenclature of medicine – clinical terms. This cohort provided a large training set to develop a natural language processing system using a random forest approach to automatically classify unstructured pathology findings into adenoma, serrated, or advanced neoplasms. This system was manually validated through an independent holdout set. RESULTS: The training set comprised 35,953 unstructured pathology reports with matched systematized nomenclature of medicine – clinical terms from 95,188 unstructured colonoscopy reports. The final model was assessed on an independent holdout set of 337 manually annotated procedures obtaining an area under the receiver operating characteristic curve of 0.997 (confidence interval [CI] 0.994–1), 0.99 (CI 0.98–1), and 0.99 (CI 0.98–0.99) for prediction of adenoma, serrated, and advanced lesions, respectively. DISCUSSION: The random forest-based hybrid natural language processing system for classification of colonoscopy results was both accurate and explainable. NLP combined with effective machine learning algorithms can provide a scalable strategy for colonoscopy quality monitoring.

Abstract Introduction: Lutetium-177 DOTATATE peptide receptor radionuclide therapy (PRRT) is an effective treatment for gastroenteropancreatic neuroendocrine tumors (GEP-NETs). While generally well tolerated, PRRT can result in hematologic toxicity ranging from mild cytopenias to therapy-related myeloid neoplasms (t-MNs). Understanding the incidence, severity, and clinical consequences of hematologic toxicity is essential for optimizing treatment decisions and establishing effective monitoring strategies. This study aimed to characterize hematologic toxicity patterns, severity, and recovery profiles in GEP-NET patients treated with Lutetium-177 DOTATATE PRRT and to determine the frequency of cytopenia-related treatment discontinuation. Methods: We conducted a retrospective analysis of 160 consecutive GEP-NET patients who underwent PRRT. Hematologic parameters (hemoglobin, white blood cell count, absolute neutrophil count, platelet count, and lymphocyte count) were assessed at baseline, mid-treatment (post-cycle 2), and post-treatment (post-cycle 4). Cytopenias were graded using Common Terminology Criteria for Adverse Events version 4.03 and categorized as never (grade &lt;2 throughout), transient (grade ≥2 mid-treatment, resolving post-treatment), persistent (grade ≥2 at both timepoints), or late-onset (grade &lt;2 mid-treatment, grade ≥2 post-treatment). Treatment completion rates and discontinuation reasons were documented. Results: Overall, 73% of patients (117/160) completed all planned PRRT cycles. Among the 43 patients who discontinued treatment early, only 4 (2.5% of total cohort) discontinued specifically due to cytopenia, while the remainder discontinued for other reasons. Post-treatment grade ≥2 cytopenias were uncommon: lymphocytes (4.4%), hemoglobin (2.5%), neutrophils (1.9%), white blood cells (1.3%), and platelets (1.3%). The majority of patients (≥85%) never experienced grade ≥2 cytopenia throughout treatment. When cytopenias occurred, they were predominantly transient (8-10% of patients) with complete recovery by treatment completion. Persistent cytopenias were rare (&lt;5% across all cell lines), while late-onset cytopenia occurred most frequently with neutrophils (14%). Conclusion: Lutetium-177 DOTATATE PRRT demonstrates an excellent hematologic safety profile in GEP-NET patients. Severe cytopenias are uncommon, predominantly transient, and rarely necessitate treatment discontinuation. These findings support the continued use of PRRT in appropriate candidates, with cytopenia-related discontinuation occurring in fewer than 3% of cases. Long-term follow-up remains essential to monitor delayed hematologic effects, including t-MNs. Future research should evaluate baseline predictors such as prior chemotherapy, renal function, and marrow reserve to identify patients at higher risk who may benefit from closer hematologic surveillance.

Abstract Background: Polycythemia vera (PV) is a myeloproliferative neoplasm characterized by red blood cell overproduction. In the phase 2 REVIVE study (NCT04057040), rusfertide was superior to placebo in achieving hematocrit (Hct) levels &lt;45% and reducing or eliminating the need for therapeutic phlebotomy (PHL) in patients (pts) with PV who were PHL dependent prior to study entry (Kremyanskaya M, et al. N Engl J Med. 2024;390(8):723-35). During the open-label extension portion of REVIVE (Part 3), combining rusfertide and PHL with or without cytoreductive therapy (CRT) controlled erythrocytosis, provided long-term control of Hct, and was associated with a greater than 8-fold reduction in the estimated annual PHL rate (Gerds AT, et al. Blood. 2024;144(Suppl. 1):4559). Pts who participated in REVIVE Part 3 were eligible to transition to the open-label phase 2 THRIVE extension study (NCT06033586) and receive up to 2 additional years of rusfertide treatment. Our objective is to present initial results describing the long-term durability of response and safety profile of rusfertide in pts with PV who participated in REVIVE and transitioned to THRIVE. Methods Pts with PV who participated in REVIVE, completed ≥12 months of rusfertide therapy, and had an end-of-treatment visit were eligible to transition to THRIVE. Pts who enrolled in THRIVE continued to receive subcutaneous rusfertide once weekly with or without CRT. Median Hct and the number of PHLs each pt received were assessed in all pts who received ≥1 dose of rusfertide and had ≥1 efficacy assessment on study. Safety data were also collected, including treatment-emergent adverse events (AEs), serious adverse events (SAEs), non-PV malignancies, and thromboembolic events (TEs). New-onset AEs (ie, AEs that were reported in THRIVE but not REVIVE) were also recorded. Results: Forty-six/58 pts (79%) who enrolled in Part 3 of REVIVE transitioned to THRIVE. At the data cutoff date (27 May 2025), 44 of the 46 pts (96%) who enrolled in THRIVE remained on study. Median (range) age was 58 (27-77), and the majority were male (74%). More than half (57%) had high-risk PV; 54% of pts were on concurrent CRT. Median (range) treatment duration in THRIVE was 48 (22-66) weeks; median (range) treatment duration in REVIVE and THRIVE combined was 198 (154-267) weeks, or 3.8 (3.0-5.1) years. At baseline, mean (standard deviation [SD]) Hct was 42.3% (3.7) in THRIVE. At Week 60, mean (SD) Hct was 43.0% (4.2). In addition, mean hemoglobin and erythrocyte levels remained stable throughout THRIVE. Prior to study entry in REVIVE, the mean (SD) annualized PHL rate (ie, PHL/year) for the 46 pts who eventually rolled over to THRIVE was 9.2 (5.2) PHL/year. The mean (SD) annualized PHL rate during REVIVE Part 3 and THRIVE was 0.6 (0.8) and 0.7 (1.1) PHL/year, respectively. Overall, the most common AEs in the pts who participated in REVIVE and THRIVE were Grade 1-2 injection site reactions (87%), fatigue (59%), COVID-19 (50%), pruritus (44%), arthralgia (39%), dizziness (35%), anemia (30%), paresthesia (28%), headache (26%), abdominal pain and nausea (24% each), and diarrhea, dyspnea, and upper respiratory tract infection (22% each). In THRIVE, the most common new-onset AEs were anemia (20%) and fatigue (15%). Twelve pts (26%) had a prior history of non-PV cancer. Six pts (13%) had a new-onset cancer event, including basal cell carcinoma (n=3; 7%), squamous cell carcinoma (n=2, 4%), non-invasive bladder cancer (n=1, 2%), and multiple myeloma (n=1; 2%). Of these 6 pts, 5 (83%) had a prior history of non-PV cancer. Nine pts (20%) had a history of TEs prior to enrolling in REVIVE. One patient with cardiovascular risk factors and a TE prior to enrollment in REVIVE had a new-onset TE of cerebrovascular accident in THRIVE. Overall, there were no TEs in pts with low-risk PV in either REVIVE or THRIVE. Conclusions: After transitioning to THRIVE, continued treatment with rusfertide with or without CRT demonstrated consistent, long-term Hct control with reduced therapeutic PHLs compared to baseline. With a median of 3.8 years of treatment, rusfertide's safety profile was consistent with prior observations. Support Protagonist Therapeutics, Inc.

Abstract Introduction While outcomes in patients with R/R FL have improved with T-cell–redirecting treatments (e.g. CAR T-cell therapy, bispecific antibodies), there remains an unmet need for safe, efficacious, and more convenient chemotherapy-free treatment options (Caridà et al, Eur J Haematol. 2025). GOLCA is a potential, first-in-class, oral CELMoD agent designed for the treatment of lymphoma, with preferential distribution to lymphoid organs and enhanced activity in lymphoma cell lines. GOLCA drives the closed, active conformation of cereblon to induce rapid and deep degradation of Ikaros and Aiolos, leading to direct cell killing (agnostic of cell of origin) and immunomodulatory activity. In the two-part, multicenter, first-in-human Phase 1/2 study (CC-99282-NHL-001; NCT03930953), GOLCA was well tolerated and effective in patients with R/R FL (Cordoba et al, ICML 2025, #441). Here, we provide longer follow-up in patients with R/R FL from Part B of the study. Methods Patients with R/R FL with ≥ 2 prior lines of therapy (≥ 1 in Part B if prior anti-CD20 therapy) were included in the study. Patients received GOLCA monotherapy orally, once daily at different dosing schedules in Part A. In Part B, GOLCA was dosed at 0.2 or 0.4 mg (14 days on/14 days off) ± R. Total GOLCA treatment duration was up to 2 years or until progressive disease (PD)/unacceptable toxicity. Primary objectives included safety and recommended Phase 2 dose determination. Results As of April 3, 2025, a total of 72 patients with R/R FL were enrolled: 12 in Part A (GOLCA monotherapy) and 60 in Part B Cohort D (22 received GOLCA 0.2 mg + R; 38 received GOLCA 0.4 mg + R). Patients were heavily pre-treated. Median number of prior treatments was 4.5 (range, 2–6) in Part A and 3 (range, 1–12) in Part B Cohort D. Approximately one-third of the treated patients were exposed to prior T-cell–redirecting therapy, approximately one-third had prior lenalidomide (len) exposure, and approximately one-third were refractory to the last regimen received. At the time of data cutoff, in Part A, 4 patients completed 2 years of GOLCA, remaining in remission at last follow-up; 8 discontinued due to PD. In Part B Cohort D, 41% of patients treated with 0.2 mg and 63% with 0.4 mg were ongoing. PD was the most common reason for discontinuation. In the safety evaluable population (n = 60; GOLCA 0.2 or 0.4 mg + R), neutropenia, an on-target side effect of GOLCA, was the most common grade 3/4 treatment-emergent adverse event (TEAE) and occurred in 65% of patients, followed by anemia (13%) and febrile neutropenia (8%). Serious AEs related to GOLCA occurred in 22% of patients, most commonly infections (17%) and febrile neutropenia (7%); pulmonary embolism occurred in 1 patient with 0.2 mg. The most common causes of GOLCA interruption in the overall safety population were infections (32%) and neutropenia (18%). Dose reductions were mostly due to neutropenia (10%) and febrile neutropenia (5%). No discontinuations or deaths occurred from GOLCA-related TEAEs. Non-hematologic TEAEs were infrequent and mostly low grade, with the most common being gastrointestinal disorders (7%). In the efficacy evaluable patients (n = 56; GOLCA 0.2 or 0.4 mg + R) at a median follow-up of 10.8 months, the overall response rate (ORR) was 89% (complete response rate [CRR], 61%). With 0.2 mg, ORR was 81% (CRR, 43%) and with 0.4 mg, ORR was 94% (CRR, 71%). In the 0.4-mg group, responses were consistent in high-risk subsets, including patients with prior len (ORR, 100%; CRR, 73%) and/or T-cell–redirecting therapy (ORR, 91%; CRR, 64%). With GOLCA 0.4 mg, 10 patients had response lasting &gt; 12 months, including 5 with prior T-cell–redirecting therapy and 6 with prior len. Conclusions With additional follow-up, GOLCA + R continued to show promising efficacy with durable responses and no new safety signals. A higher ORR/CRR and similar tolerability were observed with GOLCA 0.4 mg + R vs GOLCA 0.2 mg + R, including in patients with prior len-based and/or T-cell–redirecting treatment. These data support continued development of GOLCA 0.4 mg + R as a fixed-duration, chemotherapy-free, outpatient option in the ongoing Phase 3 GOLSEEK-4 study in 2L+ FL (NCT06911502).

Abstract Introduction: Autologous CD19 CART therapies have been utilized across a wide range of B cell driven autoimmune diseases (AD), including systemic lupus erythematous (SLE), idiopathic inflammatory myopathies (IIM), systemic sclerosis (SSc), & myasthenia gravis (MG). To date, a number of autologous CD19-CART therapies have delivered durable drug free responses in AD patients. However, the safety profile of autologous CD19-CART therapies across different AD has yet to be fully explored. This is especially true for CRS & ICANS. Here, we provide novel insight into the mechanism underlying the safety profile of resecabtagene autoleucel (rese-cel) an autologous CD19 41BBz CART therapy across four separate Phase I/II clinical trials in SLE, IIM, SSc, & MG. Objectives: The primary objective of each trial is safety & tolerability of rese-cel at Day 29. Key secondary objectives include changes in clinical scores & use of immunomodulatory agents. Key translational assessments include CART cell pharmacokinetics (PK), impact on peripheral B cell populations (pharmacodynamics), & serum cytokine levels. Methods: 19 Patients (data cutoff: 6/2/2025 SLE; 5/6/2025 IIM, SSc, and MG), with active disease refractory to standard of care have been treated across 4 Phase I/II clinical trials in SLE (8 patients; NCT06121297), IIM (8 patients; NCT06154252), SSc (2 patients; NCT06328777), & MG (1 patient; NCT06359041). All patients were treated with a single weight-based infusion of rese-cel at a dose of 1 x 106 cells/kg following lymphodepletion (flu 25 mg/m2/d on Days -5, -4, & -3, & cy 1,000 mg/m2/d on Day -3). All non-glucocorticoid immunomodulatory agents were stopped prior to lymphodepletion. Glucocorticoids were tapered post-infusion. Patients were not given prophylactic tocilizumab pre-infusion. Translational assessments were determined as follows: CART PK was evaluated by flow cytometry & dPCR; B-cell enumeration & phenotyping were evaluated by flow cytometry; & serum cytokines were evaluated via immunoassay. Results: Across all indications (19 patients), 7 episodes of CRS were observed (7/19). 6 of 7 patients experienced a Grade 1 CRS, & 1 patient had a Grade 2 CRS. 2 patients developed ICANS; 1 patient had a Grade 4 (previously presented at ACR Convergence 2024), & the other patient had a Grade 3. Both ICANS events were rapidly resolved without sequelae using standard therapy. These CRS and ICANS events differed across indications. In IIM, 4 of 8 patients experienced Grade 1 CRS and no patients experienced ICANs. In SLE, 2 patients experienced Grade 1 CRS and one developed Grade 4 ICANs. In SSC, 1 of 2 patients experienced Grade 2 CRS & the other experienced Grade 3 ICANS. In MG, no CRS or ICANS was observed. Rese-cel infusion products were ~ 66% transduced, with a mean CD4:CD8 ratio of 6. Post-infusion, peak CART expansion was observed on day 12 & the mean peak expansion was 89 cells/µL (SD +/- 214). B cells were rapidly depleted from peripheral blood post-infusion, with nadir occurring at 13 days & repopulation beginning at 62 days post-infusion on average. Re-emergent B cells were largely of the CD24+CD38+ transitional naïve phenotype. Commensurate with B cell depletion, serum BAFF induction was observed, with a mean fold induction of 16 & mean peak level of 56,404 pg/µL (SD: +/- 45,547). Serum cytokines associated with CRS & ICANS; IFNg, IL6, & IL8 reached peak elevation on days 10, 9, & 10 respectively post-infusion. The mean peak elevation for IFNg, IL6, & IL8 were 232 pg/ µL (SD: +/- 320), 44 pg/ µL (SD: +/- 60), & 80 pg/ µL (SD +/- 73), respectively. Conclusion: Rese-cel appears to be well tolerated in autoimmune patients with rates of CRS & ICANS of 37% & 11% across all autoimmune indications, respectively (SLE patients had a 25% CRS rate & 12.5% ICANS rate, IIM patients had a 50% CRS rate & 0% ICANS rate, SSC patients had a 50% CRS & 50% ICANS rate, & MG patients had a 0% CRS & ICANS rate). Notably, the frequency & severity of CRS appears to be low, with no CRS in 63% of patients (12/19) & most CRS events (6/7) being Grade 1. The lower frequency & severity of both CRS & ICANS events are likely correlated with the relatively modest induction of serum IFNg, IL6, & IL8 found in autoimmune patients post rese-cel weight-adjusted dose infusion. High BAFF levels reflect deep systemic B cell depletion. Together, these data support further support late-stage clinical development of rese-cel in autoimmune disease.

Abstract Introduction Histiocytic neoplasms (HN) are a rare, heterogeneous group of hematologic disorders derived from myeloid-dendritic cell lineages. The most common forms include Langerhans cell histiocytosis (LCH), Erdheim-Chester disease (ECD), and Rosai-Dorfman disease (RDD). These disorders are driven by recurrent activating mutations in the MAPK pathway, most frequently involving BRAF, MAP2K1, PIK3CA, KRAS, and NRAS. This discovery enabled a major therapeutic advance with the use of BRAF and MEK inhibitors, resulting in durable responses. For patients harboring KRAS mutations, MEK inhibitors (MEKi) remain the primary therapeutic approach. However, the impact of KRAS mutation subtypes on treatment response remains poorly understood. Our study aimed to characterize the spectrum of KRAS mutations in LCH, ECD, and RDD and evaluate the responses to MEKi, providing insights to guide future treatment strategies. Methods We conducted a retrospective review of patients with LCH, ECD, and RDD who were evaluated at Mayo Clinic or University of Alabama at Birmingham. Patients were included if next-generation sequencing identified a KRAS mutation. The response assessment was based on radiographic evaluation under the most recent Histiocyte Society consensus guideline. Results We identified 23 patients with a KRAS mutation: 17 females (73.9%) and 6 males (26.1%), with a median age at diagnosis of 61 years (range, 20–78). RDD accounted for 73.9% (17/23) and ECD for 26.1% (6/23); no KRAS mutations were detected in LCH patients. The most frequent KRAS variants were p.K117N (34.8%), p.G12D (17.4%), p.A146T (13.0%), p.G13C (8.7%), and p.G13D (8.7%), with additional variants including p.T58I, p.A59G, p.A146P, and p.A146V. Mutation distribution differed by disease group: p.G12D was more common in ECD (50%) than RDD (5.9%) (p=0.01), whereas p.K117N occurred in 47.1% of RDD and was absent in ECD. Regarding treatment, 57% (13/23) received MEKi, all initially cobimetinib, with 1 patient switched to trametinib due to progression. Of the 10 patients who did not receive MEKi, 1 was treated with vemurafenib for a concurrent BRAF p.V600E mutation; 3 remained on observation; 2 underwent surgery without recurrence; 3 received other systemic therapies including corticosteroid, methotrexate, rituximab, lenalidomide, or sirolimus; and 1 developed diffuse large B-cell lymphoma, treated with R-CHOP. The overall response rate in the 12 patients on MEKi (excluding 1 patient too early for assessment) was 75%—3 (25%) CR and 6 (50%) PR (including 1 who initially progressed on cobimetinib but responded to trametinib). All 3 non-responders had RDD. Among the 5 patients with p.K117N, 3 had no response to cobimetinib, 1 achieved PR, and 1 achieved CR; notably, 1 non-responder switched to trametinib and achieved PR in 2 months. All 3 patients with codon 146 mutations achieved PR. Of the 2 patients with p.G12D, 1 achieved CR with a co-occurring MAP2K1 mutation, and 1 had no response. No additional genotype–response patterns were observed. Similar heterogeneity has been reported in prior studies. In a phase II cobimetinib trial, an ECD patient with p.R149G achieved PR, whereas another ECD patient with p.G12R and an LCH patient with p.G13C achieved CR in the presence of co-occurring ARAF and NRAS mutations, respectively. A retrospective cohort described an ECD patient with p.K117N achieving PR on dabrafenib and trametinib with a concurrent BRAF mutation and another with p.G12A achieving PR on trametinib. In a multicenter analysis of trametinib, a patient with p.A59T (co-occurring BRAF and NRAS mutations) had no response, whereas another with p.A146P achieved PR. Collectively, these findings, together with our data, underscore that KRAS-mutated histiocytoses exhibit heterogeneous responses to MEKi, likely influenced by variant type and co-mutations. Discussion KRAS mutations represent an important subset of MAPK pathway alterations in HN, although their prevalence varies by disease type and appears extremely rare in LCH, with no cases identified in our cohort. The most common variants include p.K117N and p.G12D, which may be linked to suboptimal response to MEKi in the absence of concurrent MAPK pathway alterations. As MEKi acts downstream, efficacy likely depends on the level of pathway activation conferred by specific KRAS variants. Larger studies are needed to confirm these observations and identify mutation-specific predictors to guide personalized treatment.