A gastric carcinosarcoma with neuroendocrine cell differentiation and undifferentiated spindle-shaped sarcoma component possibly progressing from the conventional tubular adenocarcinoma; an immunohistochemical and ultrastructural study.

A 56-year-old Japanese man underwent total gastrectomy with lymph-node dissection for a gastric tumor. In the oral rim of the excised large ulcerated tumor, a small nodular mass demonstrated a unique histology of a carcinosarcoma composed of more than three distinctive components. A major part of the large ulcerated tumor tissue consisted of conventional tubular adenocarcinoma, with the coincidental focal distribution of solid cell nests of poorly differentiated or neuroendocrine cell (small cell) carcinoma. Sarcoma cells were another of the constituents of the small nodular tumor with atypical spindle-shaped cells. All the excised lymph-node metastasis demonstrated the histology of tubular adenocarcinoma. In the sarcoma cells, many of the lineage-specific immunohistochemical markers were negative. Only vimentin was positive. Electron microscopy revealed that the neuroendocrine cell carcinoma contained cells with abundant small aggregations of neurosecretory-type granules in their cellular cytoplasm. Primitive cellular junctions and incomplete basal lamina were seen in the sarcoma cells. No transitional or hybrid-type cells were seen between carcinoma and sarcoma cells. The interfaces between the cancer cell nests and the proliferation of sarcoma cells are clearly discerned. It was speculated that the unique histology of carcinosarcoma might have progressed from the conventional type of pre-existing advanced tubular adenocarcinoma.