Citations

ABSTRACT High dose melphalan (HDM) with autologous stem cell transplant is an established treatment for systemic light chain amyloidosis, but its incremental benefit in the era of effective standard intensity therapy is unknown. We retrospectively analyzed 475 transplant‐eligible patients who completed standard intensity treatment with or without HDM within 12 months at six centers in Europe and the United States between 2010 and 2024 to evaluate outcomes by baseline risk factors, hematologic response, and receipt of HDM. Death was an equally competing risk after the 12‐month landmark chosen to address early non‐proportional hazards and to ensure completion of first‐line therapy. BMPC > 20% was associated with inferior outcomes (HR 1.7), and gain/amp 1q with shorter TTP (HR 2.15), whereas other high‐risk FISH abnormalities were not. In multivariable models, VGPR/CR after standard intensity therapy was associated with longer TTP (HR 0.49/0.29), while gain/amp 1q remained independently associated with shorter TTP (HR 2.18). Receipt of daratumumab and HDM were associated with longer TTP (HR 0.44/0.61). HDM benefited patients who had not achieved CR after standard intensity therapy (mTTP 21.0 vs. 5.7 months without HDM), whereas patients already in CR did not benefit. Higher BMPC at diagnosis was associated with earlier progression in patients not receiving HDM (HR 1.9 for 5%–20% and 4.09 for > 20%), a risk attenuated in the HDM cohort. Gain/amp 1q remained associated with shorter TTP regardless of HDM exposure. These findings support a selective role for HDM, primarily benefiting patients with residual disease after standard intensity therapy or higher BMPC burden at diagnosis.

ABSTRACT Talquetamab is a GPRC5D × CD3 bispecific antibody approved for relapsed/refractory multiple myeloma (RRMM). This is the first real‐world study to comprehensively report muco‐cutaneous toxicities, infections, and efficacy of talquetamab in 151 patients across five countries with the longest follow‐up reported enabling better efficacy and toxicity estimates. The median age was 64 years; high‐risk cytogenetics were present in 42%; ECOG ≥ 2 in 22%; 12% had creatinine clearance < 30; and 55% would not have met MonumenTAL‐1 eligibility. Patients received a median of 6 prior lines of therapy, 53% were penta‐refractory, and 75% received prior BCMA therapy. Talquetamab was associated with skin toxicity in 39.7%, nail toxicity in 75.5%, dysgeusia in 60.4%, and oral toxicities in 62.9%, with grade ≥ 3 events uncommon (≤ 4%) and dose interruptions infrequent (9.6% for skin toxicity, 6.9% for dysgeusia, and 4.0% for oral toxicities). These findings underscore the need for improved supportive care for muco‐cutaneous toxicities. In multivariate analysis, only platelet count < 50 (HR 1.8, 95% CI 1.15–2.83) was associated with inferior PFS, while penta‐refractory status, absolute lymphocyte count < 0.4, and prior BCMA‐targeted therapy were not statistically significant. With a median follow‐up of 12.7 months, the overall response rate was 67.6%, median progression‐free survival was 7 months, and 12‐month overall survival was 65%. This study shows that talquetamab efficacy is maintained in a heavily pretreated real‐world population with high prior BCMA exposure and notable comorbidity burden.

Abstract Solitary bone plasmacytoma (SBP) and SBP with minimal marrow involvement (SBPmm) are treated similarly with definitive radiation therapy (RT) followed by observation. However, differences in the natural disease course after RT between the two, are not well described. We performed a multicenter study assessing outcomes after RT in 141 patients with SBP and 102 with SBPmm diagnosed between January 2010 and December 2024. About 92% of patients with SBPmm progressed to multiple myeloma (MM) vs 76% of those with SBP (P = .01). Among patients with SBP, 21% progressed with a second solitary bone lesion vs 4% with SBPmm (P&lt; .01). Patients with longer time to progression (TTP) after initial RT could achieve durable responses with RT to a second solitary plasmacytoma in the absence of other myeloma-defining events (MDE). Multifocal lytic bone lesions were the most common MDE, occurring in 89% and 81% of patients with SBPmm and SBP, respectively. Patients with SBPmm had a median TTP of 15 months (95% confidence interval [CI], 14-21) compared to 43 months (95% CI, 34-55) for those with SBP (P&lt; .0001); 67% with SBPmm progressed within 2 years of diagnosis. Del(17p) and 1q+ (gain or amplification) were associated with shorter TTP to MM in SBPmm, with 2-year progression rates of 100% and 82%, respectively. We report significant differences in risk and modes of progression between SBP and SBPmm. Patients with SBPmm are at particularly high risk for early progression to MM, with most developing bone disease as the MDE. These findings support prospective studies incorporating frontline systemic therapy for SBPmm.

Abstract Gastrointestinal (GI) involvement is a clinically relevant but undercharacterized manifestation of systemic light chain amyloidosis (AL). We aimed to define the clinical spectrum, histologic patterns, and outcomes of symptomatic GI involvement in AL. We retrospectively analyzed 4396 patients with AL from 2010 to 2024, of whom 521 (11.9%) had provider-attributed symptomatic GI involvement; 66% had biopsy-proven GI AL. Symptoms most commonly included early satiety (61%), bowel irregularities (58%), nausea (35%), abdominal pain (28%), and dysphagia (23%). Autonomic neuropathy was frequent (43% clinician attributed; 23% via autonomic reflex testing) and contributed to dysmotility-related symptoms, often without GI biopsy positivity. Among 747 GI biopsies, mucosal infiltration predominated (71%) and was associated with bleeding (22% vs 9%), cachexia, and inferior survival, whereas vascular involvement was associated with lower bleeding risk. Combined involvement of mucosa, submucosa, and vessels conferred the worst prognosis (median overall survival [mOS], 2.4 vs 5.1 vs 7.8 years for 3 vs 2 vs 1 layer); mOS was 6.8 years and was primarily driven by cardiac stage and hematologic response (very good partial response [VGPR] or better: hazard ratio, 0.20; 95% CI 0.13-0.32), with more favorable outcomes in patients with isolated GI involvement. Cachexia and persistent diarrhea were the main drivers of morbidity, need for nutritional support, and GI-related mortality (odds ratio, 2.7 for the combined end point). GI bleeding rarely recurred after achieving VGPR or better. Overall, mucosal involvement, cachexia, and dysmotility define clinically meaningful GI AL and support systematic assessment of autonomic dysfunction as well as evaluation of the need for nutritional support as a GI-specific end point for AL trials.

Abstract Systemic light chain amyloidosis (AL) arises from monoclonal immunoglobulin light chains, but determinants of progression from precursor states remain poorly defined. In a cross-sectional cohort comprising 1950 systemic AL patients diagnosed 2010-2024, 258 (13.2%) patients with a previously diagnosed plasma cell disorder (PCD) were compared to patients with no prior PCD diagnosis. Patients with monoclonal gammopathy of undetermined signficance (MGUS) and smoldering multiple myeloma (SMM) in the former group had lower difference between involved and uninvolved FLCs (dFLC), higher M-protein, and lower rates of t(11;14) at AL diagnosis. Patients developing AL from SMM had a shorter time to AL (median 34.2 versus 61.3 months) and higher dFLC (median 28.9 versus 11.0 mg/dl) compared to those from MGUS. Patients developing AL after known multiple myeloma (MM) or lymphoplasmacytic lymphoma (LPL) commonly lacked deep hematologic response before AL (≤ very good partial response in 78% of MM, 100% of LPL patients). We additionally studied longitudinally followed cohorts of 3,966 MGUS and 426 (SMM) patients with longitudinal FLC measurements and matched follow-up, in which 1.8% of MGUS and 7.2% of SMM patients developed AL. Those patients who developed AL showed markedly higher dFLC at MGUS/SMM diagnosis and more frequent λ restriction and rates of t(11;14). Higher dFLC was associated with progressively earlier AL development; a 10% cumulative risk occurred at 20 months for patients with a dFLC >80 mg/dL but was not reached if dFLC <10 mg/dL at an estimated median follow-up of 86 months. In multivariable analysis, dFLC >6.4 mg/dL (HR 11.3) and λ isotype (HR 3.6) independently predicted AL, whereas heavy chain secretion was associated with lower risk (HR 0.2 for IgG). These findings indicate that AL risk is primarily driven by cumulative light chain exposure, refining our knowledge of AL pathophysiology and providing guidance for follow-up of patients with elevated dFLC.

Abstract Recent therapeutic advances, including bispecific antibodies (bsAbs), have improved outcomes for patients with relapsed/refractory multiple myeloma (RRMM). However, early mortality (EM) remains a significant challenge, even in the era of novel immunotherapies. We conducted a multicenter, retrospective analysis of real-world patients with RRMM treated with commercial bsAbs to evaluate the incidence and causes of EM. Between May 2022 and June 2025, a total of 441 patients were treated across 7 countries. EM, defined as death within 12 months of therapy initiation, occurred in 148 patients (34%), with a median time from bsAb initiation to death of 2.87 months (interquartile range, 1.38-6.85). The leading cause of EM was progressive disease (72%), followed by infection (13%); regardless of the cause of death, 82% had active disease at the time of death. Our findings highlight that despite encouraging efficacy, EM remains high among real-world bsAb recipients, emphasizing the need for improved disease control strategies and supportive care interventions.

Abstract Introduction: Elranatamab (Elra) is a bispecific antibody (BsAb) targeting BCMA that is approved for patients with triple class exposed relapsed refractory myeloma (RRMM) on the basis of the MagnetisMM-3 phase 2 trial. For BCMA naïve patients, an overall response rate (ORR) of 61.0% and median progression free survival (PFS) of 17.2m was observed with a median overall survival (OS) of 24.6m. However, efficacy and safety information in the real world is lacking. Methods: This was an international retrospective study of patients with RRMM treated with Elra monotherapy outside of clinical trials. Data was collected through the International Myeloma Foundation Immunotherapy Database from 7 countries (UK, USA, Canada, Greece, Spain, Czech Republic and Singapore). High-risk cytogenetic abnormalities (HRCA) were defined as 1q+, t(4;14), t(14;16), t(14;20), and/or del(17p). Response was assessed using IMWG consensus criteria. Patient characteristics were summarized by frequency (percentage) or median (range). PFS, OS were evaluated using the Kaplan-Meier method and reported with 95% confidence intervals. Results: 79 patients were included. Median age was 67 years (range: 41-95y) with 20% ≥75 years. Racial distribution was: 75% White, 16% Black/African American, 8% Asian/Pacific. 55% were ECOG performance status (PS) 1-2. Patients received a median of 5 prior lines (range 1-11), and 35% were BCMA exposed (9% CAR-T, 5% ADC, 7% BsAb, 8% BsAb plus CAR-T, 4% ADC plus BsAb). Of those with available data, 45% had HRCA,13% had extramedullary disease (EMD) and 32% had penta-drug refractory RRMM. Overall, 48% would not have been eligible for the MagnetisMM-3 trial. Median follow-up was 6.3m (range 0.5-35.0). ORR was 53% (PR 11%, VGPR 33%, CR 8%, sCR 1%) and 67% for BCMA naïve patients. Responses were significantly lower for BCMA exposed patients (ORR 31%) but did not differ by age (51% &lt;75yrs vs 60% ≥75yrs). On univariate analysis, prior BCMA exposure, platelets &lt;50, presence of HRCA and penta-refractoriness were significantly associated with a lower response rate. PFS for the whole cohort at 6 and 12m was 64% (95%CI, 54-77%) and 52% (40-67%); for BCMA naïve patients, it was 77% (65-90%) and 67% (54-84%), respectively. Within the whole cohort, PFS was shorter for: BCMA exposed (median 4.0m vs not reached (NR)), platelets &lt;50 (2.0 vs 21.7m), HRCA (7.2m vs NR), penta-refractory (4.3m vs NR). PFS did not differ significantly by EMD, PS, age, or creatinine clearance. OS for the whole cohort at 6 and12m was 74% (64-85%) and 58% (45-74%); for BCMA-naïve patients, it was 80% (43-85%) and 70% (57-87%), respectively. Within the whole cohort, OS was shorter for: BCMA exposed (median 10.3m vs NR), platelets &lt;50 (4.3m vs NR), HRCA (10.7m vs NR) and penta-refractory (10.3m vs NR). Univariate regression analysis demonstrated that prior BCMA exposure, platelets &lt;50 and penta-refractoriness were significantly associated with a worse PFS and OS, and HRCA predicted poorer survival CRS was observed in 41% of patients (grade(G)1: 35%, G2: 5%, ≥G3: 0%) with most occurring with the first step up dose (SUD): SUD1: 29%, SUD2: 15%, full dose: 4%. Tocilizumab was used in 20% and steroids in 3%. ICANS was observed in 4 cases (5%): G1: 2, G2: 1, G4: 1. Treatment was with steroids (n=3) and tocilizumab (n=2). G3-4 thrombocytopenia was observed in 19% and 14% required platelet transfusions. G3-4 neutropenia occurred in 25% with overall 31% requiring GCSF. Infections were reported in 33 (42%) patients with median time to infection of 41 days. A total of 94 infection episodes were observed over 581 personal months. There were 2 infection-related deaths reported (1 had IVIG, 1 did not). 64% had hypogammaglobulinemia (IgG &lt; 400mg/dl) and IVIG was given in 65% of patients. Conclusions: In this first international real world analysis, Elranatamab achieved a response rate of 67% and a 12m PFS of 67% in BCMA naïve patients, similar to the MagnetisMM-3 trial despite almost half not meeting trial eligibility. However, prior BCMA exposure, platelets &lt;50, high risk cytogenetics and penta refractory status were predictors of poorer outcomes. Acknowledgements: The International Myeloma Foundation, International Myeloma Working Group (IMWG)

Abstract In this study, we investigated tumor intrinsic mechanisms of resistance to cevostamab, a bispecific T-cell engager targeting Fc receptor-like protein 5 (FCRL5) and CD3 that has shown promising clinical activity and durable responses in advanced MM. Longitudinal bone marrow aspirates from nine MM patients treated with cevostamab were analyzed. All patients had previously been treated with both immunomodulatory drugs (IMiDs) and proteasome inhibitors (PI) and eight patients had received daratumumab prior to cevostamab, which was, on average, the 6th line of treatment (mean treatment duration 220±273 days). Five of nine patients responded with ≥PR. Whole genome and transcriptome sequencing was performed on sorted CD138+ MM cells at baseline, and whole exome and transcriptome sequencing was performed on five and three samples, respectively, following cevostamab discontinuation. Baseline FCRL5 expression levels did not correlate with clinical response. However, in one non-responder patient, FCRL5 expression increased four-fold after 28 days of treatment. Given the location of the FCRL5 gene on chromosome 1q—commonly amplified in advanced MM—we evaluated the presence of Gain(1q) in our study cohort. All patients whose best response was ≤PR (n=6) harbored a Gain(1q), whereas it was absent in those who achieved VGPR and sCR (n=3). Crucially, one of the patients that achieved sCR was initially treated with 60 mg of cevostamab for one year and then escalated to a higher dose cohort (90 mg) in the second year. At progression, a clonal FCRL5E115A missense mutation (allelic frequency = 56%) and a subclonal FCRL5G455Efs*19(allelic frequency = 5%) frameshift deletion mutation were detected, both absent at baseline. The missense mutation was located on the extracellular domain of FCRL5 targeted by cevostamab. To validate the functional impact of FCRL5E115Aand FCRL5G455Efs*19 on the sensitivity to cevostamab in vitro, we generated a FCRL5 knockout (KO) model utilizing CRISPR-Cas9 technology in OPM2 MM cells. In vitro cevostamab cytotoxicity assay with PBMCs and pan T cells from healthy donors at various effector to target (E:T) ratios confirmed a complete loss of cevostamab sensitivity in our FCRL5KO models. cDNA encoding patient-derived FCRL5 alterations (FCRL5E115Aand FCRL5G455Efs*19) as well as FCRL5wtwere cloned into mammalian expression vector and reintroduced into FCRL5KO cells. Cevostamab sensitivity was reinstated by FCRL5wt expression in KO cells. In contrast, FCRL5E115A conferred complete resistance to cevostamab (p&lt;0,001) and FCRL5G455Efs*19 depicted a significant decline in cevostamab sensitivity relative to FCRL5wt expressing models. Additional experiment utilizing direct stochastic optical reconstruction microscopy (dSTORM) are ongoing to monitor the membrane localization of FCRL5 mutants. By integrating genomic, transcriptomic and functional data with clinical outcomes, this work is the first to report on acquired FCRL5 mutations causing resistance to cevostamab. We hypothesize that the prolonged treatment duration may have contributed to the acquisition of the target mutations and note a subsequent durable sCR response to BCMA-targeted immunotherapy in the same patient, suggesting immune-related factors such as T cell exhaustion, were not drivers of cevostamab resistance. Due to the limited sample size, these findings require validation in larger cohorts. Nonetheless, our findings begin to elucidate tumor intrinsic mechanisms associated with cevostamab resistance.

Abstract Background: BCMA- and GPRC5D-targeting immunotherapies including CART cell therapy and Bispecific antibodies are currently approved for the treatment of multiple myeloma. However, clinical outcomes after dual antigenic exposure remain undefined. Herein we report the first report of BCMA-GPRC5D dual targeted multiple myeloma (DEMM). Methods: We conducted a retrospective multi-center study of RRMM patients treated with both BCMA- and GPRC5D-targeted treatments (TT) (CAR T, bispecific antibodies, ADCs) between November 1, 2022, and July 1, 2025. Outcomes included PFS1 (post-dual exposure), and overall survival (OS). Kaplan-Meier estimates and event-free probabilities were calculated. Results: One hundred and fifty patients who underwent TCE treatments were included and 49 patients met the criteria for inclusion. Median age was 65 years, 22.4% had creatinine clearance &lt;=30 and ECOG 2 or greater was present in 22.2%; 57% had high-risk cytogenetics (IMWG 2016), and 60.5% were penta-refractory. Patients received a median of 6 prior lines of therapy (LOT) before 1st TCE and 9 prior LOT before DEMM. 65.3% received 1 TCE, 30.6% received 2 TCE and 4.1% received 3 TCE before DEMM. Similarly, 67.3% received 1 BCMA, 24.5% received 2 BCMA TT and 4.1% received 3 BCMA TT before DEMM. Prior TT included- BCMA CART (57.1%), BCMA Bispecific (57.1%), BCMA ADC (18.4%), other TCE (10.2%). The last dual exposure was GPRC5D Bispecific in 91.8%, BCMA Bispecific in 6.1% and BCMA CART in 2%. The median followup post relapse was 3.4 months (range 0.0-16 mos). The median PFS during the last dual exposure TT was 3.98 months (95% CI: 2.96–6.70). 32.7% did not receive any subsequent LOT and died due to progressive disease. 67.3% of patients had progressive MM and received next LOT. Median PFS1 was 1.77 months (95% CI: 1.28–6.21) with 3-, 6-, and 12-month event-free probabilities of 44%%, 19% and 0% respectively. Median OS was 5.7 months (95% CI: 2.53-12.16) for DEMM from the time of refractoriness to dual antigenic targets. Conclusions: Patients dual-exposed to BCMA- and GPRC5D-directed therapies have a poor prognosis, 32.7% had not received further treatment and in those who received treatment the PFS1 was less than 2 months and an OS of 5.7 months from progression. This reflects an area of high unmet need for the patients that are dual-exposed to BCMA- and GPRC5D-directed therapies. Further data on the cohort will be updated at the meeting. Acknowledgements include, the International Myeloma Foundation, IMWG.

Abstract Background: Bispecific T cell engagers (BTCEs) have transformed the treatment of multiple myeloma (MM) and B cell malignancies by redirecting cytotoxic T cells toward malignant targets. While clinical responses can be deep and durable, the immunological determinants of BTCE efficacy, and mechanisms of eventual immune escape, remain poorly understood. Regulatory T cells (Tregs), enriched early in MM, are classically immunosuppressive, but whether they are modulated by BTCEs and contribute to therapeutic outcomes has not been systematically investigated. Methods We performed longitudinal single-cell RNA/TCR/ATAC-sequencing and immune profiling of 17 newly diagnosed multiple myeloma (NDMM) patients across induction therapy. 11 patients were treated with teclistamab plus daratumumab, lenalidomide, and dexamethasone (Tec-DRD, n = 11) in the ongoing MajesTEC-5 (HD10/DSMMXX) trial (NCT05695508). As controls, patients receiving standard-of-care DRD (n = 6) were included. Functional validation used newly established NDMM plasma cell-T cell co-cultures, real-time killing assays, cytokine ELISAs, intracellular flow cytometry and arrayed quantitative PCRs of key T cell signaling pathways. Mechanistic studies employed CRISPR-mediated perturbations and combination treatments with IMiDs. Generalizability was tested using three BTCEs in vitro: teclistamab (BCMA×CD3), blinatumomab (CD19×CD3), and glofitamab (CD20×CD3) to redirect primary human Tregs towards MM (MM.1S), lymphoma (Raji), and B-ALL (NALM-6) cell lines. Non-targeting BTCEs as well as anti-CD3 antibodies were used as controls. Preclinical in vivo studies used an immunocompetent, transplantable Bcma+ Vk*MYC tumor model treated with murinized BTCE surrogates and IMiDs. Results BTCE therapy induced robust transcriptional and epigenetic reprogramming of bone marrow Tregs into a FOXP3lowIL2RAlow cytotoxic phenotype (“exTregs”) expressing NKG7, GZMA/B, TBX21, and CCL5. In contrast, this Treg phenotype conversion was absent in DRD-treated controls. Although comprising only ~2% of marrow-infiltrating T cells, exTregs mediated direct plasma cell lysis in vitro, strictly dependent on BTCE-mediated antigen-specific synapse formation and not recapitulated by CD3 stimulation alone. IMiDs synergized with BTCEs by destabilizing the suppressive Treg phenotype via Helios (IKZF2) downregulation, augmenting granzyme and cytokine production. Single-cell ATAC-seq of Tregs isolated from Tec-DRD-exposed trial participants revealed increased chromatin accessibility at AP-1 motifs and we confirmed BATF/JUNB-driven AP-1 signaling as a central transcriptional axis orchestrating Treg effector conversion in vitro. This cytotoxic reprogramming was conserved across BTCEs targeting BCMA, CD19, and CD20, and validated in immunocompetent mouse models, indicating a generalizable, BTCE-driven mechanism of Treg repurposing, rather than target- or engager-specific biology. Conclusion Our findings uncover a novel mechanism by which BTCEs actively convert suppressive Tregs into cytotoxic, pro-inflammatory effectors that contribute to tumor clearance. We identified the BATF/JUNB transcriptional axis and IMiD-mediated Helios destabilization as targetable regulators of this process. These results redefine Treg function under BTCE pressure, support rational combination regimens with IMiDs, and suggest exTreg signatures as biomarkers and therapeutic targets to enhance T cell-redirecting immunotherapies across hematological malignancies.