Development of leiomyomas in female rats with an endocrine imbalance.

Smooth muscle tumors of the uterus are rare in rats. In our colony such tumors have never been found. It is true, however, that only a fraction of the colony has been allowed to reach extreme old age before autopsy. Bullock and Curtis (1) have data on over 2450 rats with cysticercus tumors and 489 rats with independent or primary spontaneous tumors. In the latter group there were 48 uterine tumors of which 2 were myosarcomas and 4 were leiomyomas. Therefore, the presence of leiomyomas in 4 of 16 endocrine imbalance female rats that had survived more than 3 years seems well worth reporting.