Jawed, Inshal

e19562 Background: Multiple myeloma is a chronic blood cancer in which patients often live for many years, yet the risk of death remains ongoing. While survival has improved over time, population-level studies that combine traditional survival analysis, advanced modeling techniques, and future burden projections are limited. Methods: We performed a population-based retrospective study using the Surveillance, Epidemiology, and End Results (SEER) database. Overall survival was evaluated using Kaplan–Meier analysis and Cox proportional hazards regression. Parametric survival modeling was conducted using Weibull regression to better characterize long-term mortality patterns. Machine-learning survival analysis was performed using random survival forests to assess the relative importance of clinical and demographic factors. Annual case counts were analyzed and projected through 2035 using time-series forecasting methods. Results: The study included 8,627 patients with multiple myeloma. Overall survival declined gradually over long-term follow-up, with approximately one-quarter to one-third of patients surviving at extended time points. Female patients experienced better survival than males. Significant survival differences were observed across racial groups, with Asian or Pacific Islander patients demonstrating the most favorable outcomes and American Indian or Alaska Native patients the poorest. In multivariable analyses, age, sex, race, and year of diagnosis were independently associated with survival. Parametric modeling closely mirrored non-parametric survival estimates and supported a time-dependent pattern of mortality. Machine-learning analysis identified year of diagnosis as the strongest predictor of survival, followed by age and race. Forecasting suggested that the burden of multiple myeloma will remain substantial through 2035. Conclusions: Multiple myeloma is associated with long-term survival but persistent mortality risk and ongoing demographic disparities. Combining traditional survival analysis with parametric and machine-learning approaches provides a more complete understanding of outcomes and highlights the sustained future burden of this disease, with important implications for clinical care and healthcare planning.

e18542 Background: Outcomes in adult acute lymphocytic leukemia (ALL) remain heterogeneous and strongly influenced by age. However, population-level survival gradients across older age strata and the future burden of disease in an aging population remain incompletely characterized. We evaluated long-term survival patterns and projected disease burden in adult ALL using national registry data. Methods: We conducted a retrospective cohort study using the Surveillance, Epidemiology, and End Results (SEER) database including adults aged 50–89 years diagnosed with ALL between 2000 and 2022. Overall survival (OS) was estimated using Kaplan–Meier methods and compared across age and racial subgroups. Multivariable Cox proportional hazards regression was performed to identify independent predictors of mortality. Temporal trends in annual case counts were analyzed and projected through 2035 using time-series forecasting methods. Results: A total of 7,298 adult ALL patients were included. OS declined progressively with advancing age, demonstrating clear stepwise separation across age strata. Compared with patients aged 50–54 years, mortality risk increased incrementally across successive age groups, reaching more than fourfold higher risk among patients aged 85–89 years on multivariable analysis. Race-based survival differences were observed on unadjusted analysis; however, these differences were attenuated after adjustment for age and clinical factors. More recent year of diagnosis was independently associated with modest survival improvement, reflecting incremental therapeutic progress. Forecasting analysis projected a continued rise in adult ALL case burden through 2035, with widening uncertainty intervals over time, indicating sustained future healthcare impact. Conclusions: Adult ALL outcomes remain strongly age dependent, with sharply escalating mortality risk among older patients despite gradual therapeutic improvements. Projections indicate a sustained and growing disease burden in the United States. These findings highlight the urgent need for age-adapted treatment strategies, improved inclusion of older adults in clinical trials, and healthcare system preparedness to address the needs of an aging leukemia population.

e16322 Background: Small intestine neuroendocrine carcinoma (NEC) is a rare, aggressive malignancy comprising less than 0.1% of gastrointestinal cancers. Population-level data remain limited, restricting understanding of long-term survival patterns, demographic disparities, and evolving disease burden. We evaluated survival outcomes, demographic predictors, and incidence trends of small intestine NEC in the United States. Methods: We conducted a retrospective population-based cohort study using SEER Research Data (17 registries, November 2024 submission). Patients diagnosed with malignant small intestine NEC (ICD-O-3 morphology code 9.3.3.1.2) between 2000 and 2022 were identified using SEER*Stat (v9.0.4.2). Variables including age group, sex, race, year of diagnosis, survival time, and vital status were analyzed in R (v4.5.1). Overall survival (OS) was estimated using Kaplan–Meier methods and compared using log-rank testing. Cox proportional hazards models identified independent predictors of OS. Annual case counts were modeled using time-series forecasting to project future incidence. Results: A total of 506 patients were included. Estimated OS was 94.4% (95% CI 92.4–96.4) at 1 year, 88.1% (85.3–91.0) at 3 years, and 82.4% (79.0–85.9) at 5 years, with a subset demonstrating survival beyond 15 years. Increasing age was associated with worse survival (log-rank p = 0.058). Significant racial differences in OS were observed (log-rank p < 0.0001). In multivariable analysis, race remained independently associated with OS. Incidence forecasting projected a modest increase in annual case burden over the next decade. Conclusions: Small intestine NEC demonstrates heterogeneous survival outcomes, significant demographic disparities, and projected growth in disease burden. These findings highlight the need for improved risk stratification, equitable access to care, and integration of molecular and treatment-level data to optimize management of this rare malignancy

e15598 Background: Immune checkpoint inhibitors (ICIs) have transformed the treatment landscape of gastrointestinal (GI) malignancies. Emerging evidence suggests that gut microbiome composition plays a critical role in modulating the efficacy of immunotherapy. Antibiotics, by disrupting intestinal microbial diversity, may attenuate antitumor immune responses and compromise ICI outcomes. We evaluated time-dependent clinical outcomes associated with antibiotic exposure using real-world data. Methods: We conducted a retrospective cohort study using a large federated real-world database (2015-2025). Adults (18–89 years) with gastrointestinal or hepatobiliary malignancies (including colorectal, gastric, esophageal, and liver cancers) treated with ICI, receiving systemic antibiotics, were compared with matched controls without antibiotic exposure. Cohorts were balanced using 1:1 Propensity score matching for demographics, comorbidities, and treatment variables. The primary outcome was all-cause mortality at 30 days of ICI initiation; the secondary outcomes were hospitalization secondary to infectious and organ-related complications, overall survival at 1 and 3 years. Pre-specified subgroup analyses were performed in older adults ( > / = 65 years). Effect estimates were reported as risk ratios( RR), hazard ratios (HR), and absolute risk differences. Survival was analyzed using Kaplan–Meier curves and Cox proportional hazards models. Results: Within 30 days, antibiotic exposure was associated with significantly increased risks of Clostridioides difficile infection (RR 2.39), pneumonia (RR 2.93), acute kidney injury (RR 1.40), acute respiratory failure (RR 2.11), and neutropenia (RR 1.18) (all p < 0.05). Absolute risk differences translated to a number needed to harm (NNH) of approximately 38 for pneumonia, 143 for acute kidney injury, and ~140 for C. difficile infection. One-month mortality was modestly higher in the antibiotic group (5.4% vs 4.5%; HR 1.22; p = 0.014). However, no significant differences in mortality were observed at 6 months, 1 year, or 3 years, and survival curves converged over time. In the subgroup analysis of adults ≥65 years, early adverse event patterns were preserved, while long-term mortality remained unchanged. One-year hospital admission rates did not differ significantly between groups. Conclusions: Antibiotic exposure is associated with substantial early infectious and organ-related harm and a small increase in short-term mortality, without improvement in long-term survival, including among older adults. These findings highlight a critical opportunity for risk-adapted antibiotic stewardship and careful reassessment of empiric antibiotic use. Key words: ICI- Immune checkpoint inhibitors, RR- Risk ratio, HR- Hazard Ratio, NNH- Number Needed to Harm.