Citations

Abstract BCMA-directed CAR T-cell and T-cell engager (TCE) therapies produce high response rates in relapsed multiple myeloma, yet most patients progress. Prior work identified TNFRSF17 alterations mediating antigen escape in up to 43% of TCE progressions. To evaluate the generalizability of these findings and examine antigen-loss-independent resistance, we performed whole-exome sequencing on 32 paired pre- and post-treatment progression bone marrow samples from 15 patients (5 CAR T, 10 TCE); two patients received both agents. TNFRSF17 alterations were infrequent and restricted to TCE recipients (one concurrent frameshift and missense mutation; two heterozygous copy-number losses); no biallelic loss or CAR T-associated events were observed. In contrast, deleterious/loss-of-function variants in NF-κB, PI3K-AKT-mTOR, and MAPK/ERK pathways were universal in pre-treatment samples and acquired or clonally enriched in 80% of patients at progression. Acquired events included loss-of-function alterations in CYLD , activating mutations in KRAS , NRAS and BRAF , and acquired TP53 mutations. In this series, antigen escape via TNFRSF17 /BCMA alteration was uncommon. Instead, pre-existing, acquired and clonally enriched pathogenic variants in NF-κB, PI3K-AKT-mTOR and MAPK cascades, together with TP53 mutation, emerged as a frequent finding. These alterations suggest that deregulation of BCMA-downstream survival signaling, enhanced proliferative fitness, and elevation of apoptotic threshold constitute antigen-loss-independent mechanisms of resistance.

Summary Iron deficiency (ID) is often overlooked in patients with haematological malignancies due to other potential aetiologies. Daratumumab, an anti‐cluster of differentiation 38 (anti‐CD38) monoclonal antibody, is commonly used for treating multiple myeloma (MM) in the upfront and relapsed/refractory settings. Although anaemia is a common haematological toxicity associated with daratumumab, the contribution of ID in MM patients has not been systematically investigated. We conducted a retrospective case–control study to evaluate the prevalence of ID in newly diagnosed MM (NDMM) patients. Cases were patients receiving daratumumab, ixazomib, lenalidomide and dexamethasone (Dara‐IRD, n = 55). We compared this group with an age‐ and sex‐matched cohort of patients with NDMM who received bortezomib, lenalidomide and dexamethasone (VRD, n = 20) as induction therapy. At 1‐year, nearly 50% of Dara‐IRD‐treated patients met the criteria for ID (ferritin <30 mcg/L) compared with none of the VRD‐treated controls. All Dara‐IRD‐treated patients had a decrease in ferritin at 1‐year from baseline compared with only 45% of VRD‐treated patients. These findings identify a marked clinical signal of ID among NDMM patients receiving daratumumab‐based treatment. Although the study design does not establish causality or exclude regimen‐related confounding, it highlights the need for increased awareness of the importance of monitoring iron status in MM patients treated with daratumumab‐containing regimens.

Abstract Measurable residual disease (MRD) is a powerful prognostic tool in multiple myeloma, but predictors of achieving MRD negativity after autologous stem cell transplantation (ASCT) are not well defined. We studied 814 patients who achieved at least a very good partial response after ASCT between January 2016 and January 2023 and underwent MRD assessment by next-generation flow cytometry. Overall, 387 (48%) achieved MRD negativity after ASCT. The presence of t(11;14) (odds ratio [OR], 2.1; 95% confidence interval [CI], 1.4–3.2; P&lt; .01) and pretransplant response less than complete remission (OR, 2.1; 95% CI, 1.2-3.7; P&lt; .01) independently predicted MRD positivity. Patients who were MRD positive had inferior progression-free survival (PFS; hazard ratio [HR], 1.99; 95% CI, 1.53-2.58; P&lt; .001) and overall survival (HR, 1.62; 95% CI, 1.10-2.28; P = .009). Despite lower MRD-negative rate, 5-year PFS was similar among t(11;14) MRD positive (58%) and patients who were MRD negative (63%; P = .12). In patients who were MRD negative, the 5-year PFS was 73% in those without ≥2 HRCA compared with 55% in those with ≥2 HRCA (HR 1.9, 95% CI 1.2–3.3; P = .01). In the MRD-positive cohort, 5-year PFS was 53% in patients without ≥2 HRCA vs 17% in those with ≥2 HRCA (HR, 2.4; 95% CI, 1.6-3.6; P&lt; .01). In addition, higher residual clonal plasma cell burden within MRD-positive disease was associated with inferior PFS (HR, 2.4; 95% CI, 1.2-6.9; P = .002). This study highlights that the presence of t(11;14) independently predicts MRD positivity after ASCT, although it does not significantly affect prognosis in this subgroup.

Solitary plasmacytomas (SPs) are rare localized tumors of clonal plasma cells, either in the bone (solitary bone plasmacytoma) or in soft tissue/extraosseous (extramedullary) with either no or with minimal bone marrow (BM) infiltration (<10% clonal plasma cells by immunohistochemistry) and no evidence of systemic involvement or myeloma defining events. Approximately 50% of SPs will progress to symptomatic myeloma within 5 years after initial definitive local radiotherapy. Increased availability of improved diagnostic and monitoring tools has increased the sensitivity of detection of additional lesions and marrow involvement and has implications for the follow-up strategy after treatment. Thus, the definitions and requirements for the diagnosis and follow-up of SPs are evolving. The diagnosis of SP requires the careful exclusion of multiple myeloma (MM) that would require systemic therapy, by using all the available methods to detect systemic disease (advanced imaging, sensitive BM assessment methods, blood and urine tests). Local radiotherapy remains the mainstay of therapy, and despite the availability of innovative drugs for MM, the clinical benefit of systemic therapy currently remains poorly defined. The International Myeloma Working Group provides here updated recommendations for the diagnosis, evaluation, treatment, and response assessment of patients with SPs, incorporating recent data and advances in diagnostic tools.

ABSTRACT Primary plasma cell leukemia (pPCL) is a rare and aggressive plasma cell disorder with inferior outcomes compared with multiple myeloma (MM). However, studies describing outcomes after first progression and subsequent lines of therapy remain limited. We retrospectively analyzed 104 patients with pPCL who progressed after first‐line therapy treated at one comprehensive cancer center between 2006 and 2024. Clinical characteristics, treatments, time to next treatment (TTNT), and overall survival (OS) were assessed using Kaplan–Meier methods. All pPCL patients received novel agent–based induction. At the time of analysis, 63% had died; median OS was 39 months. High‐risk cytogenetics were present in 71%. The median TTNT after first‐line therapy was 10 months. Symptomatic progression occurred in 29% of patients and was associated with significantly inferior subsequent OS (13 vs. 34 months) compared with those experiencing asymptomatic biochemical progression. The TTNT progressively shortened with subsequent lines of therapy (3rd line: 6 months; 4th line: 4 months; 5th line: 3 months). Notable exceptions included pPCL patients with t (11;14) treated with anti‐BCL‐2‐based regimens, who achieved a median TTNT of 13 months. Additionally, 24 patients received anti‐BCMA CAR T‐cell therapy. With a median follow‐up of 21 months, their median TTNT was 32 months. pPCL is characterized by frequent disease progression and diminishing response duration with successive therapeutic lines. Symptomatic progression portends particularly poor outcomes. Anti‐BCL‐2‐based therapy in t (11;14) disease and anti‐BCMA CAR T‐cell therapy appear to provide more durable disease control and represent important advances for the management of progressed pPCL.

e19564 Background: Risk stratification in multiple myeloma (MM) relies on baseline staging systems and cytogenetic abnormalities, yet early relapse occurs in a subset of patients despite favorable risk features. Prior studies showed that clonal plasma cell S-phase assessed by flow cytometry using the plasma cell proliferation (PCPRO) assay at diagnosis and at autologous stem cell transplantation (ASCT) identifies biologically high-risk disease. The prognostic significance of clonal plasma cell S-phase following ASCT has not been well defined. Methods: We retrospectively analyzed MM patients who underwent ASCT within one year of diagnosis between January 1, 2013, and August 31, 2024. Patients without available post-ASCT clonal plasma cell S-phase assessment were excluded, yielding 150 evaluable patients. The proportion of clonal plasma cells in S-phase was determined by DNA content between G0/G1 and G2/M peaks and reported as a percentage. S-phase was assessed at the first post-ASCT marrow evaluation at day +60 (D45–75) and/or day +100 (D76–130), using the earlier assessment when both were available. Patients were classified as low (<2%) or high (≥2%) post-ASCT S-phase. Landmark progression-free survival (PFS) analyses were performed from the post-transplant assessment. Multivariable Cox models adjusted for cytogenetic risk, maintenance therapy, disease response at transplantation, International Staging System (ISS), and age. Results: Among 150 evaluable patients, 36 (24%) had high post-ASCT S-phase (≥2%) and 114 (76%) had low post-ASCT S-phase (<2%). Median age at ASCT was higher in the high S-phase group (64.5 vs 61.0 years; p=0.063), and advanced ISS stage (II/III) was more frequent (78% vs 57%; p=0.02). Cytogenetic risk, induction regimen, depth of response at transplantation, and maintenance therapy were similar between groups. Patients with high post-ASCT S-phase had significantly inferior PFS compared with those with low S-phase (median 17.0 vs 39.7 months; p=0.0003). On multivariable analysis, post-ASCT S-phase ≥2% remained independently associated with inferior PFS (HR 1.76, 95% CI 1.00–3.09; p=0.049). In an exploratory analysis among patients with paired S-phase assessments at the time of ASCT and post-ASCT, dynamic S-phase trajectories further stratified outcomes. Median PFS was longest in patients with persistently low S-phase (low→low; 39.7 months), intermediate in those converting from high to low S-phase (high→low; 27.2 months), and shortest in patients with newly emergent or persistently high post-ASCT S-phase (low→high: 15.0 months; high→high: 11.0 months) p=0.0019. Conclusions: Elevated proliferative activity of residual clonal plasma cells following ASCT identifies a biologically high-risk subset of MM patients with early relapse. Dynamic changes in post-ASCT S-phase further refine post-transplant risk stratification.

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 Progression from monoclonal gammopathy of undetermined significance (MGUS) to multiple myeloma (MM) is driven by coordinated metabolic reprogramming within clonal plasma cells and the bone marrow microenvironment. We applied high-resolution MALDI–FT-ICR mass spectrometry imaging (MSI) to archived FFPE bone-marrow biopsies, integrated with matched bone marrow plasma metabolomics, to map spatial and systemic metabolic alterations. Spatial clustering delineated plasma-cell–rich niches, while Hill-based diversity and β-diversity metrics quantified intra- and inter-compartment heterogeneity. MM niches exhibited elevated 3-hydroxykynurenine, rewired tryptophan–kynurenine flux, and increased nucleotide and bioactive lipid metabolism associated with proliferation. Notably, some MGUS-like samples displayed MM-like metabolic niches undetectable in bone marrow plasma alone, underscoring spatial heterogeneity. Cross-compartment integration revealed conserved metabolic signatures and systemic redistribution of key metabolites, consistent with ecological reorganization and niche divergence during progression. These findings establish spatial metabolomics of biopsies as a framework to dissect intramedullary metabolic heterogeneity and enable metabolite-based risk stratification in plasma-cell disorders.