Resection of a large gastrointestinal stromal tumor in the stomach after imatinib treatment in a 90-year-old patient.

A 90-year-old woman presented with a 1-month history of progressive abdominal fullness. Contrast computed tomography (CT) showed a large 17-cm mass located adjacent to the antrum of the stomach without metastatic lesions. She underwent endoscopic ultrasound-guided fine-needle aspiration for diagnosis. Aspiration specimens revealed spindle-shaped cells positive for KIT by immunohistochemistry, with exon 11 mutations of the c-kit gene according to a genetic test. We ultimately diagnosed her with gastrointestinal stromal tumor (GIST). We judged the feasibility of imatinib treatment based on physiological and comprehensive geriatric assessments. We administered imatinib to reduce the tumor size and expected an excellent response based on genetic testing. After 5 months of imatinib administration with therapeutic drug monitoring (TDM), the tumor shrank by 42%. Six months later, there was no significant uptake of 18F-fluorodeoxyglucose on positron emission tomography. We successfully performed partial gastrectomy as conversion surgery, and she was carefully observed without any medication for 10 months after surgery. Here, we report a super elderly patient aged 90 years with a large GIST harboring an exon 11 mutation who underwent surgery after imatinib treatment with appropriate dose reduction during TDM after comprehensive geriatric assessment.