Hereditary diffuse gastric carcinoma (HDGC) accounts for 1–3% of all gastric carcinomas. Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors in the gastrointestinal (GI) tract but they comprise fewer than 1% of all GI malignancies. | Synchronous occurrence of hereditary gastric adenocarcinoma gastrointestinal stromal tumor and esophageal small cell and squamous carcinoma in situ An extremely rare case report