Synchronous gastrointestinal stromal tumor and locally advanced gastric adenocarcinoma achieving complete pathomorphological response after neoadjuvant therapy

Two rare clinical cases of synchronous gastric gastrointestinal stromal tumor (GIST) and locally advanced adenocarcinoma are presented. In both cases, complete pathological regression of gastric adenocarcinoma was achieved following different neoadjuvant therapy regimens. In the first case (74-year-old female patient D.), neoadjuvant chemotherapy with the FLOT regimen was administered for cT3N0M0 gastric cancer (stage IIB), followed by D2 gastrectomy. Complete pathological response was confirmed (ypT0N0, Becker grade 1a). Morphological examination incidentally revealed a subserosal GIST measuring 0.5 cm in diameter with absent mitotic activity and a progression risk of 0% (Miettinen 2006). In the second case (76-year-old male patient G.), within a clinical trial, neoadjuvant chemoradiotherapy (total dose 46 Gy with capecitabine and oxaliplatin) was delivered for cT3N1M0 gastric cancer (stage III), followed by D2 gastrectomy. Pathological examination demonstrated complete tumor regression (ypT0N0, Becker grade 1a) and identified a 1 cm GIST with a progression risk of 0%. The patient declined adjuvant chemotherapy and remains disease-free after 67 months of follow-up. These observations illustrate a rare combination of two tumors of distinct histogenesis in which complete pathological response of gastric adenocarcinoma to neoadjuvant treatment was achieved.