Intraabdominal desmoplastic small-cell tumor with divergent differentiation: clinicopathological findings and DNA ploidy.

Five cases of intraabdominal small-cell tumor with divergent differentiation are reported. All patients were of male sex. They were 10, 15, 20, 21, and 30 years of age at time of diagnosis, respectively. By light microscopy, the tumors consisted of small cells arranged in groups, nests, and clusters separated by a collagen-rich desmoplastic stroma. Immunohistochemical studies revealed the coexpression of mesenchymal, epithelial, and neural markers. Notably, all tumors coexpressed vimentin, cytokeratin, and desmin, the latter in a remarkable paranuclear dot-like fashion. In contrast to other authors, we did not find chromogranin. DNA image cytometry on four cases demonstrated two diploid and two aneuploid (hyperdiploid) cases. No correlation was found between ploidy and prognosis. One patient died from disease, another died from veno-occlusive disease after bone marrow transplantation, and the remaining patients are alive, but have progressive intraabdominal disease. Thus, our findings support the poor prognosis in this type of tumor.