Role of Adjuvant Chemotherapy in Resected Small Bowel Adenocarcinoma: An Exploratory Real-World Analysis of Survival Outcomes and Prognostic Factors

<b>Background</b>: Small bowel adenocarcinoma (SBA) is a rare malignancy, and the role of adjuvant chemotherapy following curative resection remains unclear owing to limited supporting evidence. In this study, we aimed to evaluate the real-world effectiveness of adjuvant chemotherapy in patients with resected SBA. <b>Methods</b>: We retrospectively reviewed data from patients with localized SBA who underwent curative resection at a single tertiary referral center in Southern Thailand between 2005 and 2024. <b>Results</b>: Of 128 patients diagnosed with SBA, 52 (40.6%) had localized disease and underwent curative resection. Among them, 29 patients (55.8%) received adjuvant chemotherapy and 23 (44.2%) were managed with observation alone. The median disease-free survival (DFS) was 18.1 and 16.2 months in the adjuvant chemotherapy and observation groups, respectively (<i>p</i> = 0.642). The median overall survival (OS) was 42.8 vs. 26.7 months, respectively (<i>p</i> = 0.179). Subgroup analyses revealed trends favoring adjuvant chemotherapy in patients with pathological T4 disease, nodal involvement, younger age, and non-underweight body mass indices. Positive surgical margins were associated with inferior DFS, and T4 stage was associated with worse OS. Disease recurrence occurred in 59% of patients, predominantly as distant metastasis. <b>Conclusions</b>: Adjuvant chemotherapy showed a trend toward improved survival, particularly in patients with high-risk features; however, these findings should be interpreted with caution given the limited sample size and retrospective design. These results highlight the importance of individualized treatment decisions and underscore the need for larger multi-institutional studies to clarify the role of adjuvant chemotherapy and identify prognostic biomarkers for this rare malignancy.