Ovarian neoplasms in F344 rats and B6C3F1 mice.

The National Toxicology Program (NTP) classification system for rat and mouse ovarian tumors is presented. The classification system is based on previous classification systems and on a review of all the primary ovarian tumors from the archives of the National Cancer Institute (NCI) and NTP Carcinogenesis Testing Programs. The relative frequency and principal diagnostic features of 204 ovarian tumors from 39,851 female F344 rats and 587 ovarian tumors from 41,102 female B6C3F1 mice are 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%).