Clinical characteristics and treatment outcomes for metastatic early-onset small bowel adenocarcinoma treated with first-line chemotherapy.

796 Background: Small bowel adenocarcinoma (SBA) is an aggressive rare cancer with its incidence on the rise. Although early-onset SBA (EO-SBA: diagnosed at < 50 years old) accounts for approximately 10% of all SBA, characteristics and survival outcomes of advanced EO-SBA remains under-evaluated. This study aims to evaluate clinical features and treatment outcomes of patients with advanced EO-SBA receiving first-line chemotherapy. Methods: We retrospectively analyzed the clinical data of patients who received fluoropyrimidine plus oxaliplatin as first-line treatment for recurrent or metastatic SBA at our hospital between January 2012 and July 2024 Patients were divided into two groups: those who were diagnosed at age of < 50 years old (EO-SBA) and those who were diagnosed at age of ≥50 years old (late-onset SBA, LO-SBA). Clinicopathological characteristics and treatment outcomes (objective response rate [ORR], progression-free survival [PFS], overall survival [OS], and adverse events [AEs]) were compared between two groups. Survival outcomes were estimated using the Kaplan–Meier method and compared by the log-rank test. Hazard ratios (HRs) and 95% confidence intervals (95%CIs) were calculated by univariable and multivariable Cox regression analyses. Results: A total of 69 patients (EO-SBA 18, LO-SBA 51) were included in this study. Compared to the LO-SBA group, the EO-SBA group were more likely to have non-duodenum tumor (89% vs. 49%, p = 0.002), lesser number of metastatic sites (≤2, 100% vs.78%, p = 0.007), and prior resection of primary tumor (83% vs 49%, p = 0.008). The EO-SBA group had longer PFS compared to the LO-SBA group (median PFS: HR = 0.32 [95% CI 0.12 - 0.85] p = 0.022). The EO-SBA group had a trend of longer OS compared to the LO-SBA group (median OS: HR = 0.39 [95%CI 0.15 - 1.01] p = 0.053). Age group was not identified as an independent prognostic factor for OS (HR = 0.63 [95% CI: 0.21 - 1.85], p = 0.40) and PFS (HR = 0.47 [95% CI: 0.16 - 1.37], p = 0.17) by multivariable analyses adjusted for previously reported prognostic factors (performance status, liver metastasis, primary site, histological classification, prior resection of primary tumor, and carcinoembryonic antigen [CEA] elevation). Among patients with measurable lesions (EO-SBA 9, LO-SBA 41), the EO-SBA group showed a numerically higher ORR compared with the LO-SBA group (63% vs 29%, p = 0.07). There were no significant differences of AE frequencies between two groups except for anemia (grade 3/4. EO-SBA 0% vs LO-SBA 22%, p < 0.001). Conclusions: Our study indicates the difference of clinical characteristics between two age groups in patients with advanced SBA. EO-SBA was not identified as independent prognostic factor for OS and PFS in patients treated with first-line chemotherapy.