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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.

7543 Background: Delayed neurotoxicity (DNT) after ciltacabtagene autoleucel (cilta-cel) is associated with severe morbidity and mortality occurring in 10-15% of patients. A high post-infusion peak absolute lymphocyte count (ALCpeak ≥3x10 9 /L; ALC hi ) is correlated with an increased risk of DNT (25-30%). We previously examined prophylactic dexamethasone (PPX DEX) administered for 3 days when ALC hi was reached and found no reduction in ALC expansion, DNT incidence or severity. Here, we report the use of prophylactic cyclophosphamide (PPX CTX) on ALC kinetics and DNT. Methods: We conducted a retrospective analysis of patients (pts) treated with cilta-cel at Mayo Clinic (09-12/2025; n =60). Pts with ALC hi received CTX 500 mg IV/PO once (n = 22). Outcomes and ALC kinetics including ALCpeak, ALC D28 (ALC D28 ), and area under the curve D1-D28 (ALC AUC ) were compared with PPX DEX cohort (12/2024-08/2025; n =50) and a historical cohort without PPX (04/2022-11/2024; n =116). Results: Pre-lymphodepletion (LD) demographics were similar across historical ALC hi , PPX DEX, and PPX CTX groups. Pre-LD CRP was higher in the historical ALC hi cohort; however, baseline ferritin, CRS, and ICANS, and disease burden did not differ significantly between groups. There were no statistically significant differences in time to ALCpeak or ALC kinetics among the 3 cohorts. Among pts with ALC < 3×10⁹/L treated during the PPX CTX study period, 2 developed cranial nerve palsy (IEC-CNP; 2/38, 5%). Both presented with unilateral facial nerve palsy and were treated with corticosteroids. One pt resolved symptoms by one month, while the second had persistent symptoms at 2 weeks and remains on follow-up. Among ALC hi patients in the PPX CTX cohort, DNT occurred in 4/22 pts (18%), including 1 case of IEC-CNP (5%) and 3 with parkinsonism (IEC-PKS, 14%). Within the PPX CTX cohort, baseline characteristics and post-infusion CRS or laboratory parameters did not differ between patients with and without DNT. Among patients who developed DNT, ALC kinetics were similar across PPX CTX, PPX DEX, and historical cohorts. PPX CTX was well tolerated, with 2 cases of grade 1 nausea reported. The incidence of DNT did not differ significantly between the PPX DEX (14/61, 23%) and PPX CTX (4/22, 18%) cohorts. However, DNT presentations in the PPX CTX cohort appeared milder and were responsive to treatment. Two of three patients (67%) presented with mild symptoms (one with dynamic dysphasia; second with flat affect) that responded to DEX. A third patient presented with typical parkinsonian features (hypomimia, bradykinesia, rigidity) and demonstrated clinical improvement following high-dose CTX. Conclusions: PPX CTX was well tolerated. While it did not significantly impact ALC expansion kinetics or DNT rates, first few cases of IEC-PKS suggest that the presentation may be milder and amenable to less toxic treatment. Larger cohorts are needed to refine optimal prophylactic strategies.

7514 Background: Iberdomide (Iber) is a CELMoD that binds with greater specificity & affinity to the cereblon protein of the E3 ligase complex than a traditional IMiD. Both transplant-eligible (TE) & ineligible (TIE) patients (pts) with newly diagnosed multiple myeloma (NDMM) are currently treated with quadruplet induction, consisting of an anti-CD38 monoclonal antibody, a proteasome inhibitor, an IMiD & dexamethasone (dex). We conducted a clinical trial (NCT05392946, IDEAL) to examine the efficacy of a novel finite-duration approach, using Iber, daratumumab, bortezomib & dex (Iber-DVd) quadruplet induction followed by Iber monotherapy maintenance. Methods: Both TE and TIE pts with NDMM were enrolled in this Phase 1 (3+3 design)/Phase 2 (single stage) trial. The primary goal was to assess the ≥complete response (CR) rate — utilizing the more sensitive serum MASS-FIX assay in lieu of serum immunofixation — during induction. Treatment involved twelve 28-day cycles of induction with Iber, given PO at the recommended phase 2 dose (RP2D), days 1-21, daratumumab 1800mg SQ, weekly for 2 cycles, every other week during Cycles 3-6, & every 4 weeks thereafter, bortezomib 1.3 mg/m 2 SQ, weekly & dex 40 mg, weekly, followed by Iber monotherapy (24 cycles). Growth factor was not allowed during the dose-limiting toxicity (DLT) assessment period (Cycle 1). Results: Among 47 pts enrolled, 9 pts were in Phase 1 portion which assessed the maximum tolerated dose (MTD), with Iber starting at 1 mg/day dose, days 1-21 [Dose Level (DL) 1]. DLT (all grade 4 neutropenia) was noted in 3 pts, 2 at DL 1 & 1 at DL -1. This analysis includes 44 pts who received Iber at the RP2D (0.75 mg/day, days 1-21), including 6 pts from the Dose Confirmation Cohort (Phase 1, DL -1), dosed at MTD, & 38 pts in the Dose Expansion Cohort. The median age at registration was 65 years (range 36-86 years), & 23 pts (52.3%) were deemed high-risk. At data cut-off, pts had received a median of 15 cycles (range 3-36) of therapy. Overall response rate was 100%; ≥CR rate, 36.4% (95% CI: 22.4, 52.2) during induction & 52.3% (95% CI: 36.7, 67.5), overall, including the maintenance phase. The marrow flow-based (10 -5 ) MRD negative rate was 29.5% during induction & 47.7% overall. At a median follow-up (FU) 18.3 mos, 2 pts have died (one during FU due to progressive disease & the other on-treatment due to COVID-19). 12- (& 18-) month progression-free survival & overall survival rates were 91% (88%) & 97% (94%), respectively. Most common toxicities at RP2D were lymphopenia, neutropenia (leading 27% of pts to require pegfilgrastim support), rash, peripheral neuropathy, diarrhea, & infections. Cases of high-grade fatigue were low (<5%). Updated data will be presented at the meeting. Conclusions: Iber-DVd is an active and safe regimen for both TE and TIE pts with NDMM, leading to high response rates which improved over time, with nearly one-half of the pts achieving MRD negative state. Clinical trial information: NCT05392946 .

7518 Background: Monoclonal gammopathy of undetermined significance (MGUS) is common, yet only a minority progress to malignant plasma-cell disorders. Mayo risk stratification uses baseline factors and is commonly implemented/validated in a Cox proportional hazards (CoxPH) framework, which may miss prognostic longitudinal patterns. Methods: We assembled 15,158 MGUS patients with longitudinal laboratory data and progression outcomes (smoldering multiple myeloma, multiple myeloma, AL amyloidosis, or Waldenström macroglobulinemia). We compared a Mayo-factor Cox proportional hazards (CoxPH) baseline versus STRaTS, a transformer-based survival model, to predict progression risk at 3-, 5-, and 10-year horizons. STRaTS leveraged longitudinal trajectories of routine labs including hemoglobin, platelets, differential counts (neutrophils/lymphocytes/monocytes), immunoglobulins (IgG/IgA/IgM), free light chains (kappa/lambda), M-spike, and creatinine. To minimize bias, we used laboratory results collected from 1–3 years after diagnosis and started follow-up at year 3; patients progressing before year 3 or lacking follow-up beyond year 3 were excluded. A total of 7,305 patients met eligibility and were split into train/validation/test cohorts of 4,383/1,461/1,461. Discrimination was assessed by concordance index (C-index). Clinical operating performance was evaluated on a held-out test cohort by comparing sensitivity and specificity at the same proportion of patients selected for intensified surveillance (same workload). Results: Among MGUS patients with complete baseline Mayo factors(N=3,388), Kaplan–Meier–estimated 3-/5-/10-year cumulative progression risk was 0.1/0.4/3.4% (Low), 3.0/4.3/7.9% (Low-Intermediate), 4.4/6.4/14.1% (High-Intermediate), and 8.9/12.5/16.9% (High). On a held-out test cohort, STRaTS demonstrated superior discrimination versus the Mayo-factor CoxPH (C-index 0.75 vs 0.538; p<0.0001). Both models were trained and evaluated on identical train/test splits. At the same surveillance workload, STRaTS achieved higher sensitivity with comparable specificity; when 40.3% of patients were selected for closer surveillance, 3-year sensitivity was 81.0% for STRaTS versus 47.6% for CoxPH (Table). Conclusions: Among MGUS patients who remain progression-free at 3 years, transformer-based survival modeling of longitudinal laboratory trajectories provides more accurate individualized conditional progression risk estimates and improved workload-matched identification of progressors compared with the conventional Mayo/Cox approach. Sensitivity/specificity (%). Operating Point Flagged % STRaTS Sens / Spec (%) CoxPH Sens / Spec (%) Int+High, 3y 40.3 81.0 / 58.5 47.6 / 58.9 Int+High, 5y 40.3 81.2 / 60.4 46.9 / 58.8 Int+High, 10y 40.3 25.0 / 56.3 23.8 / 58.7 Two-Group High (≥2 factors), 5y 5.6 37.4 / 93.4 35.4 / 93.1

1633 Background: CAR-T cell therapy has transformed outcomes of hematologic malignancies and is poised to expand into solid malignancies. However, broader use of CAR-T remains constrained by the need for timely cytokine release syndrome (CRS) detection. Current episodic monitoring may miss early physiologic changes. Wearable digital health technologies (DHTs), offering continuous monitoring and real-time alerts, could enable earlier CRS detection, further support outpatient delivery, and expand access to CAR-T and potentially other immunotherapies associated with CRS. Methods: This single-center observational study (NCT05018208) enrolled patients receiving FDA-approved CAR-T products in the outpatient setting at Mayo Clinic, Rochester MN. Management of post-CAR-T complications (e.g. CRS) followed the institution’s standard of care. Patients were monitored from day -5 to day +30 post infusion with intermittent remote patient monitoring (SoC) and an arm-worn wearable device for continuous monitoring (DHT). Patients were included in this analysis if DHT data were available for ≥ 5h of data/day or ≥ 2h of data/night on ≥2 days or nights for baseline and ≥1 day or night within 72h prior to CRS, or at least 2h within 4h of CRS onset, or if DHT was available for ≥7 days/nights post infusion with no CRS event. CRS detection time by DHT was defined as the onset of pyrexia or threshold-based deviation from an individual’s baseline pulse distributions. Results: 32 patients were included in this report (median age 64 years, gender 12 F/20 M, diagnoses 18 MM/14 NHL). 25 patients experienced a CRS event, with maximum CRS grades ranging from 1-3 (16 G1, 8 G2, 1 G3). 24/25 patients with CRS required tocilizumab/steroid. Median CRS onset time was 3.4 days (range 0.4-18.4). 12/32 patients had sufficient DHT data (7 CRS, 5 no CRS) for analysis. 5 patients with CRS had a DHT detection time in advance of the SoC by a median of 13h (range 2.8 - 69.2). The DHT prediction of CRS by baseline HR change was earlier than the first episodic fever by a median of 14.5h (range 13-77.5). The remaining 2/7 patients who did not have CRS detected by the DHT had missing DHT data for more than 45h before a treated CRS event. DHT detected CRS in 2/5 patients without CRS according to SoC. One patient had fever caught with intermittent monitoring. The other was treated for neutropenia fever with suspicion of CRS and/or infection. Conclusions: These results offer evidence that continuous DHT can identify CRS events earlier than intermittent monitoring (SoC). Despite limitations related to compliance with wearable device use and data missingness, and variability in clinical management of CRS, we highlight the usability of DHT and its potential for future studies with optimized strategies to address these limitations. Clinical trial information: NCT05018208 .

1503 Background: CAR T-cell therapy has revolutionized treatment outcomes in hematological malignancies, but has traditionally required inpatient post-infusion monitoring, which is associated with significant cost and time toxicity. Outpatient CAR T infusion and monitoring has been the standard approach at Mayo Clinic site in Rochester, MN, with demonstrated feasibility and safety (Bansal et al., ASCO 2023). We present data comparing healthcare utilization between CAR T recipients who underwent outpatient remote monitoring and those with traditional inpatient monitoring. Methods: Electronic medical records were retrospectively analyzed for 293 patients who received CAR T-cell therapy for a hematological malignancy at any of the 3 Mayo Clinic sites (MN, AZ, FL) between 2020 and 2024 . Healthcare utilization was compared between patients who received outpatient CAR T with remote patient monitoring in Rochester, MN (N = 125) and those who received inpatient CAR T in the Arizona (n = 90) and Florida (n = 78) sites. Per protocol, patients in the inpatient group underwent mandatory inpatient monitoring for 7 days, with extension per provider discretion. Data was analyzed through Chi-Square and Wilcoxon tests. P values < 0.05 were considered statistically significant. Results: There was no significant difference in baseline sex, age, ethnicity, LDH, platelets, or neutrophils among the 293 patients. Diagnoses included lymphoma (n = 175), multiple myeloma (n = 106), and B-ALL (n = 12). The most common CAR T-cell products used were axicabtagene ciloleucel (n = 138) idecabtagene vicleucel (n = 56), and ciltacabtagene autoleucel (n = 50). Median hospital days were lower in the outpatient group vs the inpatient group at 30 days (4.4 vs 13.3, P < 0.001) and 90 days (4.6 vs 13.6, P < 0.001). ICU admission occurred in 1 outpatient patient ( < 1%) vs 18 inpatient patients (11%) in the first 30 days (P < 0.001). In the first 30 days, 22% of patients in the outpatient group did not require hospitalization, while 56%, 15%, and 6% required 1, 2, and 3 hospitalizations, respectively. Similarly, only 11 (8.8%) patients in the outpatient group had ≥1 ED visit in the first 30 days compared with 32 (20%) pts in the inpatient group (P = 0.009). At 30 days, there was no difference in patient portal use, with 58% of patients using the portal at least once and a median of 1 message in both groups. Within the first 30 days, 53% and 2% of patients in the outpatient group required 1 and 2 outpatient visits, respectively, vs 29% and 2% in the inpatient group (P < 0.001). There was no difference in 30-day mortality (1.6% outpatient vs 2.4% in inpatient) between the 2 groups (P = 1.00) Conclusions: Outpatient CAR T-cell therapy monitoring was associated with significantly fewer hospital days without increased ED visits, ICU stays, portal use, or 30-day mortality. This demonstrates lower healthcare utilization for outpatient CAR-T therapy.

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.

Summary Renal response (RenR) in light‐chain (AL) amyloidosis is associated with a lower risk of end‐stage kidney disease and improved survival. However, substantial variation exists in the time to and depth of RenR. We investigated variables associated with RenR in a retrospective study of newly diagnosed AL amyloidosis patients ( n = 350) assessable for RenR between 2010 and 2022. RenRs were recorded at 6, 12 and 24 months and best response. Deep RenR was defined as a ≥renal very good partial response (RenVGPR, >60% reduction in 24‐h proteinuria or ≤200 mg). Logistic regression and competing risk methods were used to examine variables associated with RenR. The median age was 64 years, and median follow‐up was 5.5 years. On multivariable logistic regression, obtaining ≥HemVGPR within 6 months, kappa isotype, high baseline difference between involved and uninvolved free light chains (dFLC ≥40 mg/dL), renal stage and autologous haematopoietic stem cell transplant (AHSCT) were significantly associated with deep RenR. Cumulative incidence rates for deep RenR, treating death or renal progression as a competing event, demonstrated that early HemR, first‐line AHSCT, lower renal stage and dFLC ≥40 mg/dL significantly increased the likelihood of deep RenR. Specific clonal plasma cell features, namely light‐chain isotype and baseline dFLC levels, independently influence the timing and depth of RenRs in AL amyloidosis following treatment, in addition to renal stage and HemR.

Abstract Solitary plasmacytoma of bone (SPB) is a localized plasma cell neoplasm associated with a substantial risk of progression to multiple myeloma (MM), yet the role of adjuvant systemic therapy following definitive radiation therapy (RT) remains undefined. We conducted a randomized phase III trial (Alliance A061402) to evaluate whether the addition of systemic therapy with ixazomib, lenalidomide, and dexamethasone (IXA-LEN-DEX) to zoledronic acid (ZA) improves outcomes compared with ZA alone in patients with SPB and minimal (< 10%) bone marrow plasma cell involvement following RT. Patients were randomized to receive six 28-day cycles of IXA-LEN-DEX-ZA or ZA alone. The primary endpoint was time to progression (TTP) to MM. The study was closed early due to poor accrual after enrolling 11 patients (IXA-LEN-DEX-ZA, n = 5; ZA, n = 6). All patients completed RT and planned treatment without dose reductions. The combination regimen was well tolerated, with limited grade ≥ 3 toxicities, including hypophosphatemia and lymphopenia. At follow-up extending beyond 4 years, the 1- and 4-year progression rates to MM in the IXA-LEN-DEX-ZA arm were 0% and 33%, respectively, compared with 37.5% and 58.3% at 1 and 2 years in the ZA-alone arm. Although underpowered, these findings demonstrate the feasibility and tolerability of an all-oral adjuvant systemic regimen in SPB and provide prospective data supporting further investigation of systemic strategies to delay progression to MM.

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.