Concurrent Stage III Unresectable Duodenal Adenocarcinoma and Metastatic Gastrointestinal Stromal Tumor Treated With Combination of Imatinib and mFOLFIRI

Cases of concurrent duodenal adenocarcinoma and gastrointestinal stromal tumors (GISTs) are rare, and only a few have been reported. While some cases of other synchronous primary tumors with GIST have been reported, no shared mutations have been consistently found, creating challenges in selecting chemotherapy in cases of inoperable tumors. Here, we presented a case of a stage IIIA locally advanced/unresectable duodenal adenocarcinoma with concurrent metastatic small bowel GIST successfully being treated with combined imatinib and modified folinic acid, 5-fluorouracil, and irinotecan (mFOLFIRI) regimen.