Spontaneous reproductive tract leiomyomas in aged guinea-pigs.

Seven of 83 female guinea-pigs were found to have reproductive tract leiomyomas at necropsy. Sixty-three of these guinea-pigs also had cystic rete ovarii. Eleven separate leiomyomas were identified, the most common site of formation being the uterine body or horn. The tumours contained histological evidence of smooth muscle, abundant fibrous connective tissue and occasional foci of fibrocartilage and bone. Mitotic figures were identified in only one tumour. The mean age of guinea-pigs with leiomyomas was 47.6 months, and the mean age of the study population was 33.1 months. Two other reproductive tract tumours identified in the 83 guinea-pigs were an ovarian teratoma and a cavernous haemangioma. These data indicate that leiomyomas are the most common reproductive tract tumour in this colony of aged female guinea-pigs and that they are frequently seen in conjunction with cystic rete ovarii.