[Ultra-Short-Term Neoadjuvant Imatinib Leads to Curative Resection and Pathological Complete Response in a Large Invasive Gastric GIST].

According to the Japanese clinical practice guidelines, surgical resection is the first-line treatment for primary gastrointestinal stromal tumors(GISTs). However, neoadjuvant imatinib therapy is recommended for tumors >10 cm in size or those with a high risk of incomplete resection. We report a rare case of an invasive gastric GIST initially diagnosed as an unresectable tumor, in which a 12-day course of preoperative imatinib led to a marked tumor response, allowing curative surgery and achieving a pathological complete response(pCR). A 62-year-old man presented with appetite loss and a large GIST with a central ulcer in the upper gastric body. CT revealed a >15 cm mass with suspected invasion into the lateral liver segment, pancreas, spleen, and diaphragm. Neoadjuvant imatinib(400 mg/day)was administered. By day 7, CT showed significant tumor necrosis and shrinkage. However, on day 12, he developed massive bilateral pleural effusion and pneumonia, necessitating imatinib discontinuation and intensive care with mechanical ventilation. After clinical improvement, a curative resection involving proximal gastrectomy with distal pancreatectomy, splenectomy, or partial diaphragmatic resection was performed. Pathological examination showed complete disappearance of GIST cells, indicating pCR. The postoperative course was uneventful, and the patient remained recurrence-free. This extremely rare case highlights the potential of ultra- short-term imatinib therapy to induce pCR in GIST. Further molecular analyses, including mutational profiling, are required.