Undifferentiated gastric cancer confirmed by detailed pathological studies. Report of a case

Undifferentiated gastric cancer is defined as carcinoma having no adenocarcinoma or squamous cell carcinoma component in any part of the tumor focus. We herein report a case of undifferentiated gastric cancer, which is extremely rare. A 62-year-old male with hematemesis and had been admitted for examination was found to have a type 5 tumor in the upper body of the stomach based on the findings of upper gastrointestinal endoscopy. According to a histopathological examination of endoscopic biopsy tumor specimens, we suspected either small-cell carcinoma, malignant lymphoma, or undifferentiated carcinoma, but no definitive diagnosis was obtained. We therefore performed a total gastrectomy with local resection of the lateral hepatic segment and left diaphragm because the tumor involved both. Based on a histopathological examination of the resected specimen, we conducted different types of immunohistochemical staining, but only CK5/6, vimentin, and cyclinD1 demonstrated positive findings. We ultimately diagnosed the patient as having undifferentiated gastric carcinoma based silver impregnation and electron microscopy findings. Postoperative chemotherapy was conducted by S-1, and no recurrence has been observed in the 13 months since surgery. To the best of our knowledge, so far very few reports have been made on such tumors, especially including detailed pathological studies. No consensus yet exists on the prognosis and treatment of undifferentiated gastric cancer, thus calling for further studies of patients with this disease.