Green, Kimberly M

Patients with plasma cell leukemia (PCL) are generally excluded from pivotal T-cell redirecting bispecific antibody (BsAb) trials. We evaluated real-world outcomes in a multicenter retrospective study of 122 patients with primary or secondary PCL across 15 academic centers, categorized as 'active' (≥5% circulating plasma cells within 30 days of BsAb initiation) or 'historical'. In a heavily pretreated population, patients received teclistamab (37%), elranatamab (11%), talquetamab as a line of therapy (Tal LOT, 42%), or talquetamab as bridging therapy to CAR-T (Tal Bridge, 11%). Cytokine release syndrome (CRS) was grade 1-2 in 56% and grade 3-4 in 4%, whereas neurotoxicity was grade 1-2 in 16% and grade 3-4 in 5%. Among 110 evaluable patients, the overall response rate (ORR) was 55%, including 61% with Tal LOT, 58% with Tal Bridge, 46% with elranatamab, and 33% with teclistamab. With a median follow-up of 8.3 months, talquetamab demonstrated superior survival. Tal LOT showed a median progression-free survival (mPFS) of 5.5 months and a median overall survival (mOS) of 11.5 months, and both were unreached in the Tal Bridge cohort. In contrast, teclistamab and elranatamab showed a mPFS of 1.2 and 1.6 months and mOS of 8.1 and 3.6 months, respectively (P=0.007, P=0.023). In active PCL, Tal LOT achieved mPFS/mOS of 6.9/12.2 months versus 0.7/1.4 months with teclistamab and 1.0/3.1 months with elranatamab, respectively (P<0.001, P=0.002). Multivariable analysis associated active PCL with worse survival and Tal LOT with improved outcomes. BsAbs were safe in PCL, with talquetamab showing superior outcomes compared with BCMA-directed BsAbs.

Abstract Introduction: Ciltacabtagene autoleucel (cilta-cel) is a highly effective BCMA-redirected CAR T-cell therapy for RRMM. While the pivotal CARTITUDE-1 trial established a target dose of 0.75 x 10^6 CAR+ viable T-cells/kg, the approved cell dose is 0.5-1.0 x 10^6 and the optimal dosing strategy to balance efficacy and toxicity remains unclear. This question is of interest given that a dose-response association has been demonstrated for idecabtagene vicleucel (a related BCMA-directed CAR T product). It has also been hypothesized that lower doses of cilta-cel may be associated with reduced toxicity. This study aims to evaluate the association between cilta-cel dose and key efficacy and toxicity outcomes using a large, real-world dataset from the US Multiple Myeloma Immunotherapy Consortium. Methods: We conducted a multicenter, retrospective analysis of 751 RRMM patients treated with commercial cilta-cel across 15 US academic centers. The administered cilta-cel dose (million cells/kg) was categorized into four groups: low (<0.5), standard-low (0.5 to <0.6), standard (0.6 to <0.8), and standard-high (0.8 to 1.0). We compared incidence rates of cytokine release syndrome (CRS), immune effector cell-associated neurotoxicity syndrome (ICANS), delayed neurotoxicity (DNT), and immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS) across these dose categories using logistic regression. Best response rates and progression-free survival (PFS), estimated using the Kaplan-Meier method, were also compared, with differences assessed using the log-rank test for the latter. Results presented are derived from multivariable models adjusting for extramedullary disease, ECOG status, penta-refractory disease and receipt of bridging therapy. Results: Among 751 infused patients, the dose distribution was: <0.5 (n=33), 0.5 to <0.6 (n=131), 0.6 to <0.8 (n=550), and 0.8 to 1.0 (n=37). The four dose groups were well-balanced in terms of baseline patient and disease characteristics, including age, high-risk cytogenetics, and extramedullary disease, with the exception of t(14;16), which was more common in the standard-low and standard dose groups (p=0.006). There were no statistically significant differences in the rates of any grade CRS (p=0.11), any grade ICANS (p=0.84), grade ≥3 ICANS (p=0.36), duration of CRS (p=0.18) or ICANS (p=0.64), or IEC-HS (p=0.16) across the four dose categories. Time to onset of CRS was shorter for the standard-high dose compared to the low dose (6 days vs. 8 days; p=0.08). Importantly, there was no significant difference in the rate of DNT (3.0%, 9.2%, 8.8%, 5.4%; p=0.24). Similarly, there was no significant difference in overall response rates (97%, 96%, 96%, 88%; p=0.50) or complete response rates (75%, 65%, 75%, 66%; p=0.10) by dose. The median follow-up was 12.3 months (IQR: 6.9, 20.5). For patients who received a standard-low dose (0.5, 0.6), the median PFS was 17.5 (IQR: 13.5, NR) months. For the standard dose range of (0.6, 0.8), the median PFS was 28.7 (95% CI: 19.8, NR) months, while the median PFS for the standard-high dose (0.8, 1.0) was not reached. For the low dose range of <0.5, the median follow up was only 8.7 months, which did not allow reliable estimation of the median PFS. While the overall difference in PFS among the groups did not reach statistical significance by the log rank test, there was a clear trend toward improved PFS with higher cell doses in the multivariable model, with outcomes clearly ordered in the same direction as the cell dose categories. A similar trend was also evident in the rates of 12-month PFS which showed an improvement with increasing dose (62% ,67%, 73%, 80%). Conclusions: In this large, real-world cohort of RRMM patients treated with cilta-cel, a lower cell dose was not associated with reduced incidence or severity of CRS, ICANS, DNT, or IEC-HS. Conversely, a dose-response correlation with PFS was observed, with higher doses trending toward longer median and 12-month PFS. It remains unknown if a lower cell dose in the commercial setting reflects poor T cell quality, yet these findings suggest that dose reduction of cilta-cel may not be an effective strategy to mitigate toxicities and might be associated with a trend toward lower efficacy. Therefore, the standard target dose should be utilized to maximize patient outcomes and further prospective dose exploration is warranted.

Abstract Introduction: The GPRC5D-directed bispecific antibody (BsAb) Talquetamab (Talq) has shown promising results for patients (pts) with relapsed/refractory multiple myeloma (RRMM) in the MonumenTAL-1 clinical trial (Chari et al. NEJM 2022). However, there are limited data on the use of Talq in the real-world setting. Methods: All pts with RRMM who started Talq between 8/2023-3/2025 across 15 US academic centers were included. High-risk cytogenetic abnormalities (HRCA) were defined as del(17p), t(4;14), t(14;16) and/or gain/amplification 1q21. Time-to-event analyses were estimated using the Kaplan-Meier method. Toxicities including CRS and ICANS were graded using CTCAE v5.0 or ASTCT criteria. Results: A total of 484 pts were included, with a median age of 65 years (range 35-89), and 83 pts (17%) were aged ≥75 years. 20% of pts were black. 21% had baseline CrCl<40, 65% had HRCA and 29% had >1 HRCA (i.e Ultra high-risk MM). The median number of prior lines of therapy was 6 (IQR 4, 8). 50% were penta-refractory, 69% received at least one prior BCMA-directed therapy (46% CART; 32% BsAb). Prior to initiation of Talq, 11 pts (2%) had CNS MM, 29 (6%) had PCL and 126 (26%) had true extramedullary disease (EMD). 70% would have been ineligible for the MonumenTAL-1 trial. For most pts (n=405; 84%) the dosing strategy from Cycle 2 was 0.8 mg/kg every 2 weeks. and the 0.4 mg/Kg weekly dosing was used in 28 patients (6%). In 6% of pts, an additional drug was added to Talq, mostly pomalidomide (n=20) or daratumumab (n=10). 101 pts (21%) received Talq as bridging for CART. Median duration of Talq treatment was 102 days. 62% developed CRS (Grade ≥3, 2%; including one Grade 5 event). 15% developed ICANS (Grades 3-4, 4%). Steroids were used in 213 patients (44%), tocilizumab in 145 (30%) and anakinra in 9 (2%). 22 patients (5%) required ICU stay during the first cycle, for a median of 6 days (range 1-31). A total of 200 pts (41%) had infections (median 1 infection each, range 1-6), including 99 (20%) with bacterial infections, 113 (23%) viral infections and 21 (4%) fungal infections. IVIG was used in 261 pts (54%). 79% of patients (n=384) developed Talq-related oral toxicity, 55% (n=269) skin toxicity and 199 (41%) nail toxicity. 157 patients died after a median follow up of 11.5 months (mos), and the leading causes of death were MM progression (n=120) and infection (n=10). 8 pts (1.7%) developed invasive second primary malignancies. The ORR was 73%, including 46% ≥VGPR. The median PFS (mPFS) for the entire cohort was 7.8 mos (95% CI 6.9-9.4) and the 12 months PFS rate was 39%. The median OS had not been reached and the 12 months OS rate was 63%. For pts who would have been eligible for MonumenTAL-1, the mPFS was 12.2 mos (95% CI 9.7 – not reached (NR); for trial-ineligible pts, the mPFS was 6.9 mos (5.8 – 8.0; p=0.003). For BCMA-naive pts, the mPFS was 15.7 mos (11.8-NR); for BCMA-exposed pts, the mPFS was 6.8 mos (6.0-7.8; p=0.0002). For patients who received Talq as bridging prior to CART, the median PFS was NR (14.1 – NR); for those who did not receive Talq as bridging the mPFS was 6.5 mos (5.3-7.6; p<0.0001). In multivariable analyses, worse OS and PFS were associated with trial ineligibility [(HR 1.38, 95% CI 1.03-1.86; p=0.03) and (2.33, 1.31-4.14; p=0.004)], BMI<30 [(1.42,1.06-1.89; p=0.02) and (1.50, 1.01-2.22; p=0.045)] and true EMD at baseline [(1.95, 1.49-2.56; p<0.001) and (1.65, 1.16-2.36; p=0.005). On the other hand, use of Talq as bridging to CART was associated with better PFS (0.27, 0.17-0.43; p<0.001) and OS (0.13, 0.05-2.56; p<0.001). Ultra high-risk MM (1.40, 1.06-1.84; p=0.02) and baseline albumin <3 (1.68, 1.18-2.37; p=0.004) were associated with worse PFS; ECOG ≥2 (1.68, 1.18-2.40; p=0.004), and baseline Plt<50K (2.14, 1.48-3.10; p<0.0001) was associated with worse OS. Conclusions: In this large real-world analysis of 484 Talq recipients, the ORR was comparable to MonumenTAL-1 but the median PFS was shorter. This likely reflects differences in patient selection, with 70% of patients in our cohort being trial-ineligible. Patients who received Talq as pre-CAR-T bridging had superior survival outcomes. Rates of toxicities were similar to MonumenTAL-1, including >70% of patients developing dysgeusia.

Abstract Background: IEC-HS is a potentially life-threatening complication following CAR-T therapy in RRMM. Reliable diagnostic biomarkers are needed to help expeditiously identify cases to initiate prompt treatment and supportive care. Serum ferritin, a routinely available laboratory parameter, is commonly elevated in IEC-HS and has been used to identify cases. However, ferritin can also be elevated in cytokine release syndrome (CRS) or secondary to baseline tumor-related inflammation. The optimal diagnostic threshold for post-CAR-T ferritin in IEC-HS in RRMM has not been previously established. Methods: This study used data from 15 centers within the US Multiple Myeloma Immunotherapy Consortium to identify the optimal post-CAR-T ferritin threshold to distinguish RRMM patients (pts) with and without a diagnosis of IEC-HS. Receiver operating characteristic (ROC) analysis was used to determine the optimal threshold based on Youden's Index. The performance of the threshold was evaluated overall and stratified by CAR-T product (cilta-cel, ide-cel). Additional analyses included the temporal relationship of peak ferritin and IEC-HS diagnosis, the evaluation of IEC-HS criteria according to ferritin levels, comparison of IEC-HS criteria co-occurrence, and comprehensive baseline characteristic comparisons across ferritin strata. Results: Of 1502 RRMM CAR-T recipients (ide-cel, n=712; cilta-cel, n=790), 74 patients (4.9%) had a provider-determined diagnosis of IEC-HS. A post-CAR-T ferritin threshold of 7470 ng/mL was identified as optimal for distinguishing pts with and without IEC-HS (AUC 0.938). Sensitivity (0.904) and specificity (0.934) were both very high, indicating high discriminatory ability. Stratified ROC analyses showed near-identical optimal thresholds for cilta-cel (7450 ng/mL; sensitivity 0.885, specificity 0.936, AUC 0.94) and ide-cel (7470 ng/mL; sensitivity 0.952, specificity 0.933, AUC 0.95), indicating minimal impact of CAR-T product on ferritin's prognostic utility. Baseline pt characteristics (N=1,413) differed significantly by ferritin threshold. Pts above the ferritin threshold of 7470 (N=154) were younger (median 64 vs 67 years; p=0.004), more frequently male (65% vs 56%; p=0.043), had higher baseline ferritin (1,300 vs 187; p<0.001), higher ECOG at apheresis (p=0.001), more likely penta-refractory (p=0.016), had higher baseline bone marrow plasma cell burden (p<0.001), and had higher R-ISS scores (p<0.001). Evaluation of IEC-HS criteria (Hines et al, TCT 2023) demonstrated significantly higher rates of laboratory and clinical criteria, including hepatic transaminase elevation (43% vs 15%), hypofibrinogenemia (53% vs 0%), cytopenias (95% vs 81%), hypertriglyceridemia (43% vs 8%), ICANS (52% vs 23%), renal insufficiency (20% vs 0%), and soluble IL-2 receptor elevations (47% vs 4%), in pts with ferritin >7500 ng/mL compared to those with lower ferritin. Heatmap visualization revealed distinct patterns of co-occurring criteria in high- and low-ferritin groups. Assessment of the timing of peak ferritin and IEC-HS diagnosis among IEC-HS cases revealed a median difference of 0 days (IQR: -1, 0), suggesting simultaneous occurrence. Median time to max ferritin was 9 days (IQR 8,12) in IEC-HS pts compared to 8 days (IQR 5,10) in non-IEC-HS pts (Wilcoxon p<0.05). Conclusions: In this analysis of over 1500 patients, a post-CAR-T ferritin level of 7500 ng/mL robustly identifies RRMM pts with IEC-HS following either cilta-cel or ide-cel. Pts exceeding this threshold demonstrate marked enrichment in IEC-HS diagnostic criteria and significant differences in baseline characteristics, warranting further study of the role of ferritin in IEC-HS diagnosis and early intervention.

Abstract Introduction: IEC-HS is an emerging and potentially life-threatening complication in multiple myeloma (MM) patients (pts) treated with CAR-T therapies. We conducted a retrospective, multi-institutional analysis to define the features and outcomes of IEC-HS after ide-cel or cilta-cel in the real-world setting. Methods: This study used data from 15 centers within the US Multiple Myeloma Immunotherapy Consortium for patients with relapsed/refractory MM (RRMM) who received commercial cilta-cel or ide-cel. IEC-HS was defined by each center based on diagnostic criteria (Hines et al, TCT 2023). Kaplan-Meier and multivariable Cox models were used for time-to-event outcomes while logistic regression was used for categorical outcomes. Results: Of 1502 RRMM pts who received either ide-cel (n=712) or cilta-cel (n=790), 74 patients (4.9%) had a provider-determined diagnosis of IEC-HS. Product-specific incidences were 2.9% for ide-cel and 6.7% for cilta-cel. The median time from CAR-T infusion to IEC-HS onset was 9.5 days (range 2-37 days). IEC-HS-related clinical findings (Hines et al, 2024) included cytopenias (95%), elevated soluble IL-2R levels (79%), fever (76%), elevated LDH (71%, median 1,800 U/L), hypofibrinogenemia (70%), hypertriglyceridemia (65%), ICANS (63%), hepatic transaminase elevation (56%), pulmonary involvement (46%), renal insufficiency (29%), hyperbilirubinemia (22%), and hemophagocytosis in bone marrow (6%). The median interval from peak CRS to IEC-HS onset was 4 days (IQR 1–6). Some variables, such as splenomegaly and coagulopathy, were not systematically collected. Nearly all pts received pharmacologic intervention: corticosteroids (94%, n=59), anakinra (76%, n=48), tocilizumab (71%, n=45), emapalumab (13%, n=8), ruxolitinib (16%, n=10), or etoposide (3%, n=2). Only one pt (2%) did not receive any IEC-HS therapy. Among those evaluable for outcomes, 58% (n=35) improved, 12% (n=7) developed further CAR-T-related complications (e.g., recurrent IEC-HS, delayed neurotoxicity), and 30% (n=18) had no therapeutic response and died. Compared to non-IEC-HS pts (n=1,428), those with IEC-HS were younger (median age 63 vs 66), male (61% vs 57%), and more frequently received cilta-cel (72% vs 52%, all p<0.01). They had higher rates of triple-class (81%) and penta-refractory (43%) disease, greater pre-treatment bone marrow plasma cell burden (40% vs 6%), and higher baseline ferritin (1058 vs 208 ng/mL). Prior autologous SCT was less common, and advanced R-ISS stage was more prevalent. IEC-HS was associated with dramatically worse PFS and OS: with cilta-cel, median PFS was 6.5 months (mo) with IEC-HS (vs 33.1 without); for ide-cel, 8.9 vs 11.4 mo. Median OS for cilta-cel IEC-HS pts was 9.6 mo (not reached in non-IEC-HS pts); for ide-cel IEC-HS, 19.6 mo (vs 40.8 mo). Multivariable analysis confirmed IEC-HS as an independent predictor of shorter PFS (HR 1.88, 95% CI 1.29–2.74, p=0.0011) and OS (HR 2.30, 95% CI 1.39–3.83, p=0.0013). Notably, IEC-HS was not associated with lower response rates – either best CR (63.9% vs 64.0%, p=0.71) or ORR (91.8% vs 90.9%, p=0.97). Cilta-cel pts had a higher probability of achieving a deep (CR) response, regardless of IEC-HS status. Grade > 3 CRS occurred in 14% (n=3/21) of ide-cel and 15% (n=8/52) of cilta-cel IEC-HS pts, versus 2% (n=12/691) and 2% (n=13/737) in non-IEC-HS pts, respectively. Any-grade ICANS was observed in 67% (n=14/21) of ide-cel and 55% (n=29/52) of cilta-cel IEC-HS cases, compared to 26% (n=179/690) and 20% (n=148/738) in non-IEC-HS. Grade ≥3 ICANS occurred in 29% (n=6/21) of ide-cel and 26% (n=14/52) of cilta-cel IEC-HS cases, relative to 4% (n=25/690) and 4% (n=27/738) in pts without IEC-HS. Severe infections were also more common: 71% (n=15/21) of ide-cel and 53% (n=28/52) of cilta-cel IEC-HS pts experienced at least one infection, compared to 31% (n=214/691) and 29% (n=217/737) in non-IEC-HS groups. Conclusions: IEC-HS is an uncommon but severe and early complication after CAR T-cell therapy for RRMM. Despite similar ORRs with or without IEC-HS, IEC-HS was associated with significantly worse PFS and OS for both ide-cel and cilta-cel. These findings support the need for vigilant monitoring and potential preemptive treatment strategies to better manage this syndrome.

Abstract Introduction: Teclistamab is the first FDA approved BCMA-directed bispecific antibody for the treatment of relapsed and refractory multiple myeloma (RRMM). With BCMA-targeting CAR-T therapies, cytokine release syndrome (CRS) is a risk factor for cardiotoxicity. Teclistamab was associated with fatal cardiovascular adverse events (CVAEs) in a recent US pharmacovigilance database analysis, but this analysis was limited by reporting bias. Therefore, the aim of our study is to conduct a multicenter study to define the real-world incidence of CVAEs in RRMM patients treated with teclistamab. Method We performed a retrospective multi-center cohort study of patients receiving teclistamab at 5 medical centers. Baseline oncologic and cardiovascular characteristics (including vital sign and echocardiographic data) were collected. Baseline cardiovascular disease (CVD) was defined as presence of coronary artery disease, congestive heart failure, severe or symptomatic valvular heart disease, or stroke at baseline. CVAE was collected and categorized based on CTCAE v5.0 by each institution. Major adverse cardiovascular event (MACE) was a composite outcome with any of the following: congestive heart failure, asymptomatic cardiomyopathy (interval LVEF drop >10% to resultant LVEF less than 50%), coronary artery disease requiring intervention, stroke or cardiovascular death. Arrhythmia was a composite outcome with any of the following: atrial tachyarrhythmia, ventricular tachyarrhythmia or bradyarrhythmia. Median follow-up was calculated through reverse Kaplan-Meier method. Multivariable Cox regression analysis was used to define the relation between MACE and survival. Cause of death was categorized as myeloma-related death or non-myeloma-related deaths (i.e. CRS, infection or cardiovascular death). Cause-specific Cox regression was performed to define relationship between MACE and cause of death. Results In a cohort of 219 patients treated with teclistamab with median follow-up of 20.1 months, 7.3% (N=16) developed MACE, 7.3% (N=16) developed arrhythmia and 12.8% (N=28) developing any MACE or arrhythmia. MACE occurred at a median of 4.5 days (IQR 2.25-15.75 days) after teclistamab step-up. The incidence of MACE was 16.4% in patients with baseline CVD versus 2.7% in those without baseline CVD (p<0.001). Patients who developed MACE had inferior ECOG performance status (PS) (PS >=2: 62.5% vs. 27.7%; p=0.008). Additionally, baseline hemoglobin level (9 vs 10g/dL; p=0.072) was numerically lower in MACE, compared to no MACE. There was no difference in age, sex, bone marrow (BM) plasma cell burden, ferritin, C-reactive protein or LDH levels between MACE vs. no MACE group. Patients who developed MACE had lower baseline diastolic blood pressure (67.7 vs 73.8mmHg; p=0.041) and numerically lower LVEF (51.4 vs 59.3%; p=0.059; baseline echocardiogram performed in 86% of all cohort). Patients who developed MACE had similar incidences of CRS (Grade >=2: 25.0 vs 16.7%; p=0.620) and immune effector cell-associated neurotoxicity (ICANS) grade 2 or higher (12.5 vs 7.5%; p=0.812). In multivariable Cox regression analysis, MACE was independently associated with inferior overall survival (HR 2.72; 95% CI 1.41-5.25; p=0.003), after adjusting for baseline CVD, age, high BM burden, extramedullary disease, and plasma cell leukemia. In cause-specific multivariable Cox regression analysis, MACE was independently associated with non-myeloma-related death (HR: 10.77 95% CI 4.39- 26.41; p<0.001) but not with myeloma-related death (1.54; 95% CI 0.64- 3.70; p=0.336). Conclusion In conclusion, in this large, real-world multicenter study, we observed that MACE occurred in over 7% of patients following teclistamab for RRMM, typically within 2 weeks of initiation. MACE was significantly associated with increased non-myeloma-related mortality. In contrast to CAR-T therapy, CRS or ICANS were not associated with MACE, whereas majority of patients who developed MACE had ECOG PS >=2 or baseline cardiovascular disease. More studies are necessary to define mechanisms and strategies to reduce these MACE and improve survival. Patients with baseline cardiovascular disease or poor performance status may benefit from cardiovascular optimization before and during teclistamab therapy.

Abstract Introduction: The CAR-T therapies ide-cel and cilta-cel are approved for patients (pts) with relapsed/refractory multiple myeloma (RRMM). The aim of this study was to determine the incidence, subtypes, and associated risk factors for subsequent primary malignancies (SPMs) in MM pts treated with CAR-T therapy in the real-world setting. Methods: A retrospective, multicenter observational cohort study was conducted of pts who received CAR-T therapy between May 2021 and Dec 2024 at 15 centers within the US Multiple Myeloma Immunotherapy Consortium. Logistic models were used for univariable analyses of invasive SPMs (excluding non-melanoma skin cancers). Variables significant at p < 0.10 were included as candidate variables in the multivariable analysis. Time to event endpoints were analyzed using Kaplan-Meier curves. Results: Of n=1460 CAR-T recipients, median follow-up from the time of CAR-T infusion for the entire cohort, ide-cel, and cilta-cel pts was 13.1, 16.9, and 10 months, respectively. A total of 55 invasive SPMs were noted in 53 pts (SPM incidence 3.6%). The incidence rate of SPMs was 4.55 per 1,000 person-years, based on 53 SPMs occurring over 11,646.14 person-years (calculated from CAR-T to the SPM diagnosis, death, or last follow-up). Baseline characteristics were similar for pts with no SPM versus SPM including: age at CAR-T (median 67 vs 65), female (36% vs 43%), Black (13% vs 16%), prior autologous transplant (87% vs 80%), lenalidomide for ≥2 years (31% vs 27%), high risk cytogenetics (23% vs 29%), and known clonal hematopoiesis (7.5% vs 9.9%). Differences were observed in baseline characteristics among pts with SPM versus no SPM for ≥2 prior alkylator lines of therapy (LOT) (82% vs 60%, p=0.002) and median prior LOT (6 vs 5, p=0.008). There was a trend for more patients with SPMs being age ≥70 (35% vs 37%, p=0.074). Of the 53 SPMs, 26 (49%) were myeloid (MDS or AML), 19 (35.8%) were solid, 7 (13.2%) were of T-cell origin, and 1 was a B-cell lymphoma. Of the T-cell SPMs, three were of T-LGL, though one of the T-LGL pts later developed an invasive CNS T-cell lymphoma (CAR-negative). There were four cases of confirmed CAR-positive T-cell SPMs (all pts treated with cilta-cel), of which two were indolent T-cell lymphoma of the GI tract and two were cutaneous PTCL. There was no difference in total incidence of SPMs among pts who received ide-cel (total=4.4%; myeloid=2.2%, T-cell=0.04%) versus cilta-cel (total=3%; myeloid=1.4%; T-cell=0.5%) (p=0.21). Median OS from the time of CAR-T therapy was 40.8 months for pts without SPM compared to 27.6 months for pts with SPM (p=0.4). Median OS did not differ by myeloid, solid, and T-cell subgroup: 26.4, 37.2, and 24 months, respectively (p=0.21). Median time from CAR-T cell to SPM was 12 months overall, and by subtypes of myeloid, solid, and T-cell was 13.2, 9.6, and 9.6 months, respectively (p=0.74). There was no difference in time to any SPM among pts receiving ide-cel versus cilta-cel (p=0.61). An earlier time to diagnosis of myeloid SPM was observed for cilta-cel versus ide-cel (4.8 vs 20.4 months; p=0.003). Median OS from the time of diagnosis of any SPM, myeloid, solid, or T-cell SPM was 9.6, 7.2, 15.6, and not reached in months, respectively (p=0.006), demonstrating that pts diagnosed with myeloid subtype SPM had inferior OS from the time of their SPM diagnosis compared to other subtypes. The cause of death of 4/11 myeloid SPM pts was the myeloid SPM itself. In univariable analysis for the entire cohort, age ≥70 (p=0.079), ≥5 prior LOT (p=0.012), and ≥2 prior alkylator LOT (p<0.001) were associated with higher risk for SPM. In multivariable analysis, ≥2 LOT containing alkylators was associated with higher risk of SPM (p=0.005). For the univariable analysis of the myeloid subgroup, ≥2 prior alkylator LOT (p=0.016) and ≥2 years of lenalidomide maintenance (p=0.063) were associated with higher risk of SPM. In multivariable analysis, ≥2 years of lenalidomide (p=0.065) was associated with a trend toward increased risk of myeloid SPM. Conclusions: With a median follow up of 13.1 months, the incidence of developing a SPM following CAR-T in pts with RRMM was 3.6%, of which approximately half were myeloid malignancies. There was no difference in SPM incidence when comparing the two CAR-T products. Pts treated with ≥2 alkylator LOT had a higher risk of SPM in multivariable analysis and may warrant additional monitoring for SPM development.