Citations

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

7064 Background: Chimeric antigen receptor (CAR) T cell therapy has revolutionized care for relapsed/refractory diffuse large B cell lymphoma (DLBCL), yet granular delineation of real-world immune effector toxicities, organ-specific sequelae and economic burden across demographic and socioeconomic strata requires further exploration. Methods: Using the National Inpatient Sample (2017–2022), we identified adult DLBCL hospitalizations receiving CAR T through ICD-10-PCS codes. Cytokine release syndrome (CRS) [all grades - 2021–2022], immune effector cell–associated neurotoxicity syndrome (ICANS) [all grades – 2022], infections, cardiac events and acute kidney injury (AKI) were identified through ICD-10 codes. Age was stratified into 21-40, 41-60, 61-80 and >81 years. Payer groups were Medicare, Medicaid, Private and Uninsured. Races were White, African American, Hispanic and others [Pacific Islanders, Native Indians, Asians]. Chi-square analysis was performed, and multivariate regression adjusted for demographics, comorbidities, and hospital characteristics. Results: Across >11,000 weighted hospitalizations, inpatient mortality, all-grade CRS and ICANS were comparable across age, race, and payer groups (p>0.05). Inpatient mortality was numerically higher in other minor races (6.6%) vs White (3.3%), African American (3.1%), and Hispanic (0.9%; p=0.230). Any grade CRS was numerically higher in other minor races (72.5%) than in White (62.3%) and African American (60.6%; p=0.614). Any grade ICANS dispersion included 29.5% (White), 39.1% (African American), 22.5% (Hispanic) and 11.1% (Other; p=0.204). A race-specific signal for ICANS grade 5 (p=0.030) was seen, but numbers were small. Among cardiac events, arrhythmias rose from 7.6% (age 21–40 years) to 57.1% ( age ≥81 years) (p<0.001). By payer, arrhythmias were highest in Medicare (31.2%; p<0.001). Other cardiac events including myocardial infarction, stroke and cardiogenic shock were similar across groups. Pneumonia rates varied by payer, peaking in the Uninsured (23.8%; p=0.010). Sepsis and septic shock rates showed no differences. AKI (p=0.007) rates showed differences but attenuated after adjustment. Hispanic and other minor races had lower adjusted costs than White (Odds ratio [OR] 0.9, p=0.046; OR 0.8, p=0.006), while ages 61–80 had higher adjusted costs vs 21–40 (OR 1.2, p=0.023). Conclusions: In this national cohort, CRS, ICANS and mortality were similar across demographic and payer strata, indicating consistent immune effector safety. Cardiac arrhythmia rates were higher among the elderly and Medicare beneficiaries. There were lower expenditures among minor race groups and higher costs in elderly. These findings highlight discrete domains of variability and suggest intensified cardiac surveillance in elderly and equitable resource allocation to optimize outcomes with CAR-T.

7062 Background: MCL is a rare and aggressive subtype of B-cell non-Hodgkin lymphoma that remains incurable. Bruton tyrosine kinase (BTK) inhibitors are an established standard of care for R/R MCL. However, comparative effectiveness data for different BTK inhibitors for R/R MCL are limited. This study evaluated the real-world effectiveness of zanu and acala in US patients with R/R MCL based on overall survival (OS) and time to next treatment (TTNT). Methods: A retrospective cohort study was conducted using Komodo health administrative claims data. Eligible patients were adults (aged ≥18 years) with ≥2 MCL diagnoses and continuous enrollment or activities within 1 year prior to and 3 months following the index date. Patients were required to initiate monotherapy with zanu (index period: November 2019 to August 2025) or acala (index period: October 2017 to August 2025) as a second-line or later (2L+) treatment, with index date defined as the first observed claim for zanu or acala. Patients with evidence of clinical trial participation, end stage renal disease or prior stem cell transplant were excluded. Outcomes included OS (time from index date to all-cause mortality) and TTNT (time from index date to subsequent therapy with an allowable gap of 120 days). If an outcome was not observed, patients were censored at the date of last activity or enrollment end date. Survival analyses were conducted using Kaplan-Meier estimates and Cox proportional hazards models. Inverse probability of treatment weighting (IPTW) was adjusted for age, sex, US region, treatment initiation year and Charlson Comorbidity Index (CCI). Results: In total, 2219 patients (zanu, n=931; acala, n=1288) were eligible and included in the study. The mean age was higher in the zanu (72.3 years; SD, 9.4) vs acala cohort (71.4 years; SD, 9.7). Most patients were male (zanu, 71%; acala, 75%), non-Hispanic white (zanu, 73%; acala, 74%), and the mean CCI was 3.5 (SD, 3.2) and 3.6 (SD, 3.1) in the zanu and acala cohorts, respectively. Median follow-up was 14.8 and 18.2 months in zanu and acala cohorts, respectively. Median TTNT was 26.7 months for zanu and 20.8 months for acala. Median OS was not reached for zanu and was 60.6 months for acala. In the unadjusted model, zanu had a longer TTNT (HR, 0.86; 95% CI, 0.76-0.97; P =.012) and OS (HR, 0.74; 95% CI, 0.62-0.88; P <.001). After IPTW adjustment, TTNT and OS favored zanu treatment (TTNT: IPTW-adjusted HR, 0.86; 95% CI, 0.76-0.98; P =.025; OS: IPTW-adjusted HR, 0.81; 95% CI, 0.68-0.98; P =.03). Conclusions: In this real-world analysis of US health claims data, zanu monotherapy demonstrated significantly longer TTNT and improved OS compared with acala in patients receiving 2L+ therapy for MCL. These findings support zanu as an effective BTK inhibitor for R/R MCL.

7041 Background: CD20×CD3 bispecific antibodies and CD19-directed CAR T-cell therapies are increasingly used in relapsed/refractory DLBCL. CAR T therapy is associated with higher rates of CRS,ICANS, and cytopenias, whereas bispecific antibodies are often perceived as less toxic and more outpatient-friendly. Methods: We conducted a retrospective cohort study using the TriNetX Global Collaborative Network. Adult patients with DLBCL treated with bispecific antibodies (glofitamab, epcoritamab) were compared with those receiving commercial CAR T-cell therapy (tisa, liso, axi). Propensity score matching was performed on demographics, comorbidities, baseline laboratory values, and corticosteroid exposure, yielding 468 patients per cohort. Outcomes included CRS, ICANS, severe neutropenia (ANC <500/µL), and thrombocytopenia (platelets <50×10³/µL), as well as hospitalization and ICU admission at 1, 3, 6, and 12 months. Overall survival (OS) was assessed using Kaplan–Meier analysis with log-rank testing. Results: After matching, CAR T therapy was associated with significantly higher immune-mediated toxicity. CRS occurred more frequently with CAR T at 1 month (37.4% vs 22.4%), 3 months (39.3% vs 27.6%), 6 months (40.6% vs 28.8%), and 12 months (41.2% vs 29.7%) (all p<0.001). ICANS was also more common with CAR T across all timepoints (1 month: 10.5% vs 4.9%; 12 months: 12.6% vs 7.5%). Severe neutropenia and thrombocytopenia were markedly more frequent in the CAR T cohort, with neutropenia affecting 66.7% vs 12.8% at 1 month and 71.6% vs 32.7% at 12 months (all p<0.001). Despite higher toxicity, healthcare utilization was comparable. Hospitalization rates were similar between groups at 1 and 3 months (61.8% vs 66.7% and 67.1% vs 75.9%), and ICU admission rates did not differ meaningfully at any timepoint. Importantly, overall survival consistently favored CAR T therapy. Survival differences emerged early and persisted over time, with lower mortality in the CAR T cohort at 1 month (2.1% vs 9.0%), 3 months (7.7% vs 18.6%), 6 months (15.8% vs 26.7%), and 12 months (26.5% vs 35.3%), corresponding to significantly improved OS by log-rank testing at all timepoints (p<0.001). Conclusions: In this large, real-world, propensity-matched analysis of relapsed/refractory DLBCL, CAR T-cell therapy was associated with substantially higher rates of CRS, ICANS, and severe cytopenias compared with bispecific antibodies. However, these toxicities did not translate into higher hospitalization or ICU utilization. Despite a less favorable early toxicity profile, CAR T therapy conferred a consistent and clinically meaningful survival advantage from early to late follow-up. Early toxicity alone should not preclude CAR T referral in appropriate candidates, underscoring the need for optimized patient selection, sequencing strategies, and supportive care.

7028 Background: Axi-cel, autologous anti-CD19 CAR T-cell therapy, showed long-term survival and curative potential in R/R LBCL (ZUMA-1; Neelapu et al. Blood . 2023). Few studies have examined long-term outcomes beyond clinical trials. Here we report long-term real-world outcomes of axi-cel in R/R LBCL using large-sample CIBMTR data. Methods: A total of 1500 adults from 79 US centers receiving commercial axi-cel after ≥2 LOT for LBCL from Oct 2017-Aug 2020 were enrolled in a post-marketing requirement study. A protocol was developed prior to the study’s implementation, reviewed by Kite and CIBMTR. This is a secondary analysis of said study. Key outcomes were progression-free survival (PFS), overall survival (OS), time to next therapy (TTNT), disease-specific mortality (competing risks were non-relapse deaths), subsequent malignancies, and non-relapse mortality (NRM). Outcomes were analyzed descriptively. Cases with missing data were excluded separately for each endpoint. Results: As of Aug 2025, 1446 patients (pts) were included in the analysis. Median age at infusion was 62.2 y (range, 19.6-90.8: 38% of pts ≥65 y); 65% were male. Five percent of pts had ECOG PS ≥2 and 16% had high-grade lymphoma. Pts had a median of 3 (range, 2-4) prior LOT, 28% had prior autologous hematopoietic cell transplantation, and 50% received bridging therapy. At 59.7 mo median follow-up, median PFS (95% CI) was 7.9 mo (6.3-10.9) and 5-y PFS was 30% (27-32). The median OS was 25.7 mo (21.6-30.2); 5-y OS was 38% (35-41). The 5-y cumulative incidence of disease-specific mortality was 51%. Among pts who were progression-free at 2, 3, 4, or 5 y post-infusion, the OS at 6 y (95% CI) was 73% (68-78), 81% (76-86), 90% (84-94), and 94% (89-97), respectively. The median duration of response (DOR) was 25.3 mo (95% CI, 20.7-32.8) and 5-y DOR was 38% (35-41). The median TTNT was 12.2 mo and 30% did not need additional LOT at 5 y. Of pts who received subsequent salvage therapy, 12 (2%) received cell therapy, 39 (7%) received hematopoietic cell transplant, and 475 (90%) received other therapy. The 1, 2, 3, 4, and 5-y cumulative incidence of relapse (95% CI) was 49% (46-51), 52% (50-55), 54% (52-57), 55% (53-58), and 56% (53-59), respectively. No new safety signals were observed. The primary causes of death (n=864; 60%) were primary disease (540; 63%), infection (111; 13%), and organ failure (57; 7%). The 5-y cumulative incidence of NRM was 16% (95% CI, 14-18). At 5 y, 11% (95% CI, 10-13) had subsequent malignancies, mostly therapy-related myeloid neoplasms (6%) and non-melanoma skin cancer (3%); none were directly attributed to axi-cel. Conclusions: This real-world study showed sustained survival at 5 y among pts with R/R LBCL treated with axi-cel after ≥2 LOT, consistent with ZUMA-1. Infection and organ failure were common causes of NRM. These results continue to support the use of axi-cel with curative intent in R/R LBCL.

7029 Background: Mosun, a CD20xCD3 T-cell engaging bispecific antibody, is approved for relapsed/refractory follicular lymphoma after ≥2 prior lines of therapy. We report an interim analysis and PROs with Mosun SC in elderly/unfit patients with previously untreated DLBCL. Methods: MorningSun (NCT05207670) is a Phase 2, basket study of Mosun SC in patients with B-cell non-Hodgkin lymphoma. In the DLBCL cohort, eligible patients (aged ≥80 years, or 65–79 years and ineligible for chemoimmunotherapy) received outpatient Mosun SC: Day (D) 1 (5 mg), D8 (45 mg) and D15 (45 mg) of Cycle (C) 1, then 45 mg on D1 for up to 17 21-day cycles. Primary endpoint was progression-free survival (PFS) rate at 24 months. Other endpoints included overall survival (OS), objective response rate (ORR), complete response (CR) rate, change from baseline (CfB) in lymphoma symptoms as assessed by the Functional Assessment of Cancer Therapy-Lymphoma subscale (FACT-Lym LYMS; higher scores indicate improvement, a ≥3-point increase is considered clinically meaningful) and safety. Results: Forty-nine patients were enrolled, primarily from community sites (n=34). Median age was 83 years (range: 71–101). International Prognostic Index was 3–5 in 53.1% patients and 18.4% of patients had bulky disease. As of February 10, 2025, the median duration of follow-up was 12.5 months (range: 1.4–30.8). PFS and OS rates at 12 months were 71.3% (95% confidence interval [CI]: 54.8–82.7) and 74.7% (95% CI: 58.5–85.4), respectively. ORR was 73.5% and CR rate was 59.2%. Completion rates for FACT-Lym LYMS were ≥95% at baseline and remained ≥87% at each subsequent timepoint. Patients reported improvement in health-related quality of life (HRQoL) over time, demonstrated by increased mean CfB (standard deviation [SD]) in FACT-Lym LYMS scores: C4D1, 5.1 (9.8); C9D1, 5.6 (11.8); C17D1, 9.8 (11.4). Clinically meaningful improvements in lymphoma symptoms were observed in 53.1% (95% CI: 38.3–67.5) of patients. The most common any-grade adverse event (AE) was injection site reaction (53.1%; all Grade [Gr] 1/2). Gr 3/4 AEs were reported in 65.3% of patients and 8.2% experienced a Gr 5 AE (no Gr 5 AEs were Mosun related, per investigator assessment). Serious AEs occurred in 42.9% of patients. Infection AEs occurred in 49.0% of patients (Gr 1: 4.1%; Gr 2: 28.6%; Gr 3: 16.3%) and resolved in 91.7%. Cytokine release syndrome occurred in 12.2% of patients (Gr 1: 10.2%; Gr 2: 2.0%; all resolved). Updated data with around one additional year of follow-up will be presented. Conclusions: Mosun SC showed promising efficacy with manageable safety in elderly/unfit patients with previously untreated DLBCL in an outpatient setting. Clinically meaningful improvements in lymphoma symptoms suggest that Mosun SC improves aspects of HRQoL in this population. Clinical trial information: NCT05207670 .

7011 Background: Up to 40% of pts with diffuse large B-cell lymphoma (DLBCL) will relapse or have refractory disease following 1L treatment (Tx) with SOC chemoimmunotherapy regimens R-CHOP or Pola-RCHP. High risk (HR) populations include those with International Prognostic Index (IPI) score 3–5 and IPI 1–2 with either ≥1 lesion ≥7 cm or baseline LDH >1.3×ULN. GOLCA is a potential, first-in-class, oral CELMoD designed for the Tx of lymphoma, with preferential distribution to lymphoid organs and enhanced activity in lymphoma cell lines. GOLCA induces rapid and deep degradation of Ikaros and Aiolos, leading to direct cell killing and immunomodulatory activity. GOLCA 0.4 mg + R-CHOP has shown promising safety, a ≥90% minimal residual disease (MRD) negativity rate, and durable efficacy (24-mo PFS, 79%) in 1L a-BCL (Nowakowski et al, ASH 2025, 476) and is being evaluated in the Phase (Ph) 3 study GOLSEEK-1 (NCT06356129). We report initial Ph1b results with GOLCA + Pola-RCHP in 1L a-BCL. Methods: Pts aged ≥18 y with ECOG PS ≤2, IPI 0–5 (Part 2A) or 2–5 (Part 2B), and newly diagnosed a-BCL with measurable tumorous disease were included. Pts were treated with GOLCA + Pola-RCHP for six 21-day (D) cycles or until disease progression/unacceptable toxicity/study withdrawal. In dose escalation, GOLCA was dosed at 0.2 and 0.4 mg D1–7. In dose expansion, pts were randomized 1:1 to Pola-RCHP + GOLCA 0.2 or 0.4 mg. Primary endpoint: safety; efficacy was a secondary endpoint. Results: At data cutoff, 57 pts were treated with GOLCA + Pola-RCHP (0.2 mg, n=28; 0.4 mg, n=29). Median age was 63 y. Most pts had HR disease (86%) and DLBCL not otherwise specified histology (84%). For known cell of origin (COO), 47% were germinal center B cell (GCB) and 39% non-GCB by Hans algorithm. Forty-seven pts (83%) completed Tx and 52 (91%) entered the follow-up (f/u) period. Grade 3/4 Tx-emergent adverse events occurred in 95% of pts, most frequently neutropenia (86%; an on-target side effect of GOLCA) and anemia (39%). Median relative dose intensity for GOLCA and Pola-RCHP components was >95%. At 15.5 mo median f/u, end of Tx (EOT) complete metabolic response (CMR) rate was 69% at 0.2 mg, 82% at 0.4 mg, and similar across COO subtypes. EOT CMR was consistent in HR pts (65% at 0.2 mg, 83% at 0.4 mg). The 12-mo DOR and PFS rates were 92% and 88% at 0.2 mg, and 96% and 96% at 0.4 mg. In pts with both pre-Tx and EOT ctDNA analysis, 65% and 83% at 0.2 and 0.4 mg achieved MRD negativity (PhasED-Seq) at EOT. Conclusions: GOLCA + Pola-RCHP demonstrated a predictable and manageable safety profile, and addition of GOLCA did not compromise median dose intensity of Pola-RCHP. GOLCA 0.4 mg + Pola-RCHP resulted in a high rate of durable CMRs, high rate of MRD negativity, and a promising 12-mo PFS rate. These data continue to show that GOLCA + SOC regimens R-CHOP and Pola-RCHP has potential to improve outcomes in 1L HR a-BCL. Clinical trial information: NCT04884035 .

6588 Background: TET2 is the most frequently mutated gene in chronic myelomonocytic leukemia (CMML) and has been associated with favorable outcome, with recent studies suggesting a more pronounced prognostic impact in the presence of ≥2 TET2 mutations ( Csizmar et al. leukemia 2025;39:2030; Kynning et al. Br J Haematol. 2025 Nov 25. doi: 10.1111/bjh.70264 ). We sought to determine if this particular observation extended to patients with ≥3 TET2 mutations ( TET2 MUT ) and also held true in the context of recently reiterated genetic risk factors. Methods: The current study was conducted under institutional review board approved minimum risk protocols allowing retrospective patient data collection and analysis. Diagnostic criteria were according to the International Consensus Classification (Arber et al. Blood 2022. 140:1200). All statistical analyses were conducted using JMP 18 software. Results: 536 CMML patients who underwent CLIA-approved NGS testing were stratified according to the number of TET2 MUT : 221 (41%) wild-type, 148 (28%) with one, 153 (29%) 2, and 14 (2%) ≥3 TET2 MUT . Co-mutation frequencies with significant differences between one vs. two TET2 MUT included ASXL1 (46% vs. 29%; p<0.01), KRAS (7% vs. 14%; p=0.02) and SETBP1 (5% vs. 0.6%; p=0.02). Phenotypic comparisons revealed preponderance of prognostically favorable traits associated with wild-type TET2 but no significant differences between one vs. two TET2 MUT . In age-adjusted univariate analysis, transplant-censored overall survival (TCOS), calculated from the time of mutation detection, was superior in patients with one (p<0.01; HR 0.7) or 2 (p<0.01; HR 0.4) but not ≥3 (p=0.4) TET2 MUT , vs. those with wild-type TET2 . TCOS was also superior with 2 vs. 1 (p=0.02; HR 0.7) but not with ≥3 vs. 1 (p=0.7) TET2 MUT ; the results were similar when TCOS was calculated from the time of diagnosis. Multivariable analysis confirmed the survival advantage of exactly two TET2 MUT vs. wild-type TET2 (p<0.01; HR 0.5), one TET2 MUT (p<0.01; HR 0.6), or ≥3 TET2 MUT (p<0.01; HR 0.4), after adjusting for age, sex, anemia, circulating blasts ≥2%, and leukocyte count ≥13×10⁹/L. The favorable impact of exactly two TET2 MUT persisted in CMML-MD and CMML-MP and remained independent of TET2 VAF, mutation type, karyotype, and other prognostically relevant mutations. This association was sustained in the BLAST (p<0.01; HR 0.5) and CPSS-mol (p=0.02; HR 0.7) models, but not in BLAST-mol model (p=0.12). Conclusions: Mechanistic explanation for this novel observation includes the possibility that TET2 mutational categories based on mutation count reflect distinct biological states rather than having a simple linear effect. The persistence of this signal despite adjustment for established molecular and genetic risk factors supports its consideration in the development of future CMML prognostic models.

6525 Background: Venetoclax plus hypomethylating agent (Ven-HMA) is the standard treatment for unfit patients with newly diagnosed acute myeloid leukemia (ND-AML), with Ven typically administered for 28 days (d) per cycle (DiNardo NEJM 2020) . However, the optimal duration of Ven across risk groups remains unclear. We examined survival outcomes with Ven 7, 14, 21, and 28d in ND-AML, in the context of European LeukemiaNet (ELN) and Mayo Genetic risk models. Methods: ND-AML patients receiving Ven-HMA at the Mayo Clinic were retrospectively studied. Patients were stratified by ELN 2024 (Döhner Blood 2024) and Mayo Genetic risk (Gangat Am J Hematol 2025) , and analyzed using standard statistical methods. Results: 540 patients (median age 75 years, 52% de novo) received HMA with Ven for 7d ( n =33), 14d ( n =117), 21d ( n =96), or 28d ( n =294). ELN and Mayo risk distributions were 22%/35% high, 18%/56% intermediate, 60%/9% low risk, respectively. Baseline characteristics were comparable. CR/CRi rates were comparable across Ven durations, with the exception of lower CR/CRi with 7d vs 21d (p=0.04). Risk-stratified CR/CRi showed variations across Mayo and ELN groups but without significant differences based on Ven duration (Table). Allogeneic transplant rates were 15%, 18%, 18%, 20% for 7, 14, 21, 28d (p=0.86). At a median followup of 37.7 months, median overall survival (OS) differed by ELN risk (6.6, 11.9, 20 months) and Mayo genetic risk (7.8, 17.4 months, not reached (NR)), for high, intermediate, low risk (p<0.01), respectively. Median OS was comparable across Ven 7, 14, 21, 28 d (13, 13, 17, 14 months; p=0.84), with corresponding 1/3/5-year survival rates (Table). 30/60d mortality differed by Ven duration; 7d 10%/20%, 14d 7%/15%, 21d 4%/13%, 28d 4%/6%. Compared with 28d, 30d mortality was higher with 7d and 14d (p=0.07/0.03), and 60d mortality was higher with 7d, 14d, and 21d (p=0.02/0.01/0.05). OS was comparable across Ven durations within ELN intermediate/low risk and all Mayo risk groups, except among ELN high risk, patients receiving 14d Ven had inferior OS compared with 21d and 28d (p<0.01). Cumulative incidence of relapse at 1 year was similar among patients receiving 14, 21, 28d Ven (16%, 18%, 18%;p >0.1). Conclusions: Survival outcomes were comparable across Ven 7, 14, 21, 28 d in ND-AML, with outcomes driven by Mayo Genetic and ELN risk. Despite differences by Ven duration in high-risk groups, higher early mortality with 7d and 14d likely reflects treatment selection. Prospective trials are needed to establish risk adapted Ven dosing strategies. 7 (N=33) 14 (N=117) 21 (N=96) 28 (N=294) P-value CR/CRi (%) 52 63 72 65 0.19 7≠21 Mayo Risk High 33 49 58 55 0.53 - Intermediate 55 69 80 69 0.17 7≠21 Low 100 85 80 84 0.84 - ELN Risk High 33 30 57 53 0.21 - Intermediate 33 59 64 56 0.63 - Low 62 74 80 73 0.46 - Median OS (months) 13 13 17 14 0.84 - 1/3/5-year survival (%) 53/NR/NR 51/25/22 56/23/20 55/27/20 >0.1 -

631 Background: Adolescent and young adult (AYA) women with breast cancer who have not completed their desired childbearing pre-diagnosis may be more likely to decline adjuvant endocrine therapy (ET) and/or to temporarily or permanently stop ET to pursue pregnancy. Fertility counseling and use of fertility preservation strategies (e.g., oocyte/embryo cryopreservation) might impact these decisions. Methods: In the Valuing Opinions and Insights from Cancer Experiences (VOICE) Study, we investigated whether use of fertility preservation strategies were associated with ET initiation and early discontinuation amongst AYAs with fertility concerns. Eligible females were diagnosed with stage 1–3 estrogen-receptor positive breast cancer at age 15-39 during 2013-2022 and responded to a survey in 2023-2024. Those who reported that they had not completed their desired family size or had been unsure about having completed their desired family size at the time of their cancer diagnosis were categorized as having had fertility concerns. ET initiation was defined as 2+ ET prescription fills within 18 months after diagnosis. Among ET initiators, we assessed early discontinuation (defined as lack of ET prescription fill over any 180 day period until 5 years after their first ET fill date). Due to inadequate power, we did not model the relationship between oocyte/embryo cryopreservation and ET initiation. However, we did have power to assess the association between oocyte/embryo cryopreservation and ET discontinuation using multivariable Cox regression to calculate Hazard Ratios (HR) and 95% Confidence Intervals (CI). HRs for discontinuation were adjusted for age at diagnosis, stage, study site, diagnosis year, income, and children before diagnosis (yes/no). Results: Among 518 AYA breast cancer survivors, 56% (N = 290) had fertility concerns at diagnosis. Of these 290, 41% had 1+ child before diagnosis, 90% received fertility counseling, 27% froze eggs or embryos, and 10% had 1+ child after diagnosis. The majority (89%) initiated ET. Among the 32 who did not initiate ET, 7 (22%) reported that fertility concerns impacted that decision. Oocyte/embryo cryopreservation was used by 26% of ET initiators and 34% of ET non-initiators. Among the 258 ET initiators, 89 (35%) discontinued ET early. Compared to those who did not use fertility preservation strategies, patients who froze oocytes/embryos were more likely to discontinue ET (HR 1.89; 95% CI 1.18–3.05). Among those who discontinued ET, 19% had 1+ child after diagnosis (compared to 2% among those who did not discontinue ET). Conclusions: This study confirmed prior studies showing that many AYAs with breast cancer have fertility concerns, and these concerns may impact decisions about ET. In our analysis, those who cryopreserved oocytes/embryos were more likely to discontinue ET early, and a higher proportion who discontinued ET had 1+ live birth after breast cancer.