Molecular Characterization of Chinese Patients with Small Bowel Adenocarcinoma

Small bowel adenocarcinoma (SBA) is a rare malignancy of the gastrointestinal tract, and its unique location within the small intestine presents difficulties in obtaining tissue samples from the lesions. This limitation hinders the research and development of effective clinical treatment methods. Circulating tumor DNA (ctDNA) analysis holds promise as an alternative approach for investigating SBA and guiding treatment decisions, thereby improving the prognosis of SBA. Between January 2017 and August 2021, a total of 336 tissue or plasma samples were obtained and the corresponding mutation status in tissue or blood was evaluated with NGS. The study found that in SBA tissues, the most commonly alternated genes were TP53, KRAS, and APC, and the most frequently affected pathways were RTK–RAS–MAPK, TP53, and WNT. Notably, the RTK–RAS–MAPK pathway was identified as a potential biomarker that could be targeted for treatment. Then, we validated the gene mutation profiling of ctDNA extracted from SBA patients exhibited the same characteristics as tissue samples for the first time. Subsequently, we applied ctDNA analysis on a terminal-stage patient who had shown no response to previous chemotherapy. After detecting alterations in the RTK–RAS–MAPK pathway in the ctDNA, the patient was treated with MEK + EGFR inhibitors and achieved a tumor shrinkage rate of 76.33