A distinctive novel epitheliomesenchymal biphasic tumor of the stomach in young adults ("gastroblastoma"): a series of 3 cases.

This report describes 3 cases of a distinctive, hitherto unreported gastric epitheliomesenchymal biphasic tumor that differs from other biphasic tumors of the stomach and elsewhere: carcinosarcoma, biphasic synovial sarcoma, teratoma, and mixed tumor. The tumors occurred in young adults, 2 males and 1 female, of ages 19, 27, and 30 years. Two tumors were located in the greater curvature in the gastric body and one in the antrum. The tumors measured 5, 6, and 15 cm in maximum diameter, and their mitotic rates were 0, 4, and 30 mitoses per 50HPF. There were 2 components: uniform oval or spindled cells in diffuse sheets, and clusters or cords of epithelial cells occasionally forming glandular structures with small lumens. The epithelial elements were positive for keratin cocktail AE1/AE3, keratin 18, and partly for keratin 7, but were negative for keratins 5/6, 20 and epithelial membrane antigen. The spindle cells were positive for vimentin and CD10. All components were negative for CD34, CD99, estrogen receptor, KIT, smooth muscle actin, desmin S100 protein, p63, calretinin, chromogranin, synaptophysin, CDX2, and thyroid transcription factor 1. In situ hybridization for SS18 rearrangement was negative in all cases separating this tumor from synovial sarcoma. All 3 patients were alive after follow-up of 3.5, 5, and 14 years. Because these tumors have some resemblance to blastomas of other organs, we propose the term "gastroblastoma" for this distinctive, at least low-grade malignant epitheliomesenchymal tumor of the stomach.