Morphology and classification of ovarian neoplasms in F344 rats and (C57BL/6 X C3H)F1 mice.

For the updating of the National Toxicology Program (NTP) classification system for rat and mouse ovarian tumors, all the primary ovarian tumors from the archives of the National Cancer Institute and NTP Carcinogenesis Testing Programs were reviewed. The relative frequency and principal diagnostic features of 204 ovarian tumors from 39,851 female F344 rats and of 587 ovarian tumors from 41,102 female (C57BL/6 X C3H)F1 (B6C3F1) mice were described. The most frequently observed neoplasms in F344 rats were malignant granulosa cell tumors (29% of primary rat ovarian neoplasms observed), benign undifferentiated sex cord-stromal tumors (26%), benign granulosa cell tumors (16%), and benign Sertoli cell tumors (7%). The most frequent neoplasms in B6C3F1 mice were cystadenomas (24%), tubulostromal adenomas (24%), benign granulosa cell tumors (21%), and benign teratomas (8%). Ovarian neoplasms were not significantly related to treatment in rats. Tubulostromal adenomas, benign and malignant granulosa cell tumors, and benign teratomas were significantly more frequent in treated mice than in controls.