A Case of Gastric Gastrointestinal Stromal Tumor with Platelet Derived Growth Factor Receptor Alpha Mutation

Abstract

A 64-year-old man with a 9 cm gastric gastrointestinal stromal tumor (GIST) and plateletderived growth factor receptor alpha (PDGFR-alpha) mutation-positive was found in a medical checkup to have a submucosal tumor (SMT). Endoscopy showed the 9 cm SMT to be located in the lesser curvature of the posterior pyloric wall. Immunohistochemical staining of biopsy specimens were all negative for c-kit, CD34, alpha-SMA and S100. Suspecting the SMT to be gastric GIST, we conducted distal gastrectomy. Abdominal computed tomography and diffusion-weighted magnetic resonance imaging indicated that the tumor grew both inward and outward, but no liver or peritoneal metastasis was seen. Pathologically, spindle and epithelial-like cells had formed irregularly. Only CD34 immunohistochemical stein was positive, while c-kit, alpha-SMA and S100 were negative. No KIT gene mutation was detected, but PDGFR-alpha mutation D842V was identified in exon 18. The size was 85 mm and the mitotic index was two cells per 50 high-power fields. This classified the GIST into an immediate risk group. Surgery was curative, and the PDGFR-alpha exon 18 D842V mutation was imatinib-resistant, so the man was followed up without adjuvant therapy. For the postoperative treatment strategy, gene search of GIST was useful.