Genomic landscape and clinical impact of homologous recombination repair gene mutation in small bowel adenocarcinoma

Background: Small bowel adenocarcinoma (SBA) is a rare malignancy with a poor prognosis and limited treatment options. Although homologous recombination deficiency has been studied as a biomarker for other cancer types, the clinical and genomic implications of homologous recombination repair (HRR) gene mutations in SBA remain unclear.
Methods: We retrospectively analyzed the data of 628 patients with advanced or recurrent SBA from a nationwide genomic database. Patients were categorized into HRR mutation and non-HRR mutation groups and compared for their clinical and genomic characteristics including tumor mutational burden (TMB) and microsatellite instability-high (MSI-H) were compared. Treatment efficacy and overall survival (OS) were assessed based on HRR gene mutation status and primary tumor site (duodenal adenocarcinoma [DA] vs. small intestinal carcinoma [SIC]).
Results: Patients with the HRR mutations had higher frequencies of TMB and MSI-H than those without the mutation (P < 0.0001). In DA, HRR gene mutation positivity was associated with improved OS and higher overall response rates (ORR) to platinum-based chemotherapy (OS: not reached vs. 23.5 months, P = 0.040; ORR: 33 % vs. 19 %, P = 0.046), whereas no significant associations were observed with SIC.
Conclusion: HRR gene mutation may be a potential biomarker for platinum-based chemotherapy efficacy in SBA, especially in DA, highlighting the need for site-specific therapies.

© 2025 Elsevier Ltd. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/

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