An update on the electron microscopy of small cell carcinoma of the ovary with hypercalcemia

Since the first description of small cell carcinoma of the ovary with hypercalcemia in 1982, similar tumors have been reported, and more than 150 additional cases have been seen in consultation. This tumor is the most common form of undifferentiated carcinoma of the ovary in women younger than 40 years and has a poor prognosis. It is now recognized to have a large cell component in 40% of cases, and large cells occasionally predominate. The tumors are also unaccompanied by hypercalcemia in about one third of the cases. Microscopically, the most common pattern is diffuse sheets of compact cells, but clusters, cords, and folliclelike structures are also usually present as well. Mitoses are numerous. Immunostaining is almost always positive for keratin, often for vimentin, and occasionally for epithelial membrane antigen. Electron microscopy (19 cases) has revealed oval, polygonal, and occasionally elongated cells that are poorly differentiated but usually contain a moderate to large amount of dilated rough endoplasmic reticulum as their most constant cytologic feature. Junctions, including desmosomes and in some cases tight junctions, mark the cells as epithelial. The histogenesis of small cell carcinoma of the ovary is still not known, but it is usually possible to distinguish it from other small cell tumors of the ovary. Neuroendocrine cells and germ cells have been suggested as possible lineages, but the clinical and morphologic evidence is against those interpretations.