Ultrastructural analysis of small cell carcinomas of the ovary.

Small cell carcinoma (SCC) of the ovary is a rare tumor of young females, frequently associated with hypercalcemia. Eight SCC specimens from six patients, including four with hypercalcemia, were examined by electron microscopy to determine if certain ultrastructural features were consistently present to be of diagnostic value and to assess histogenesis. Each tumor had epithelial features with frequent desmosome-like junctions and partial investment with basal lamina. The most consistent and prominent finding was abundant dilated rough endoplasmic reticulum (RER) forming large vesicles filled with homogeneous granular (proteinaceous) material of variable density. RER vesicles were identified in all six primary tumors and in both recurrent and metastatic lesions. Dense-core granules of neurosecretory type were absent. None showed immunohistochemical reactivity for parathyroid hormone. The ultrastructural features of SCC are sufficiently constant to be of diagnostic value in the differential diagnosis of ovarian neoplasms. Histogenesis remains obscure.