Classification of tumors of the ovary: developmental and ultrastructural considerations.

The classification of ovarian tumors presents a difficult problem because of the great variety of tumor types that can occur. The complex structure of the normal ovary and the diversity of cell types present at different stages of development contribute to this difficulty. Developmental and ultrastructural studies have helped to clarify the problem by indicating specific cell types that correspond directly with the major tumor categories. Tumors may thus be grouped as being of epithelial, germ cell or sex cord stromal origin. The ultrastructural features of tumors in the different categories indicate common characteristics shared with corresponding cell types in the developing ovary. The findings clearly support a histogenetic approach in the classification of ovarian tumors.