Feline mammary carcinoma and progestogens.

The results of medroxyprogesterone acetate injections in cats to prevent estrus are reported. 5 cats were given 25 mg depot-medroxyprogesterone injections every 3 months for an average period of 5 years. Of these 2 developed adenocarcinoma of the breast at 4 and 2 years, respectively, after the last injections. Histologically, the tumors resembled human cancers. These tumors are rare in cats. The mean time for the appearance for the evaluation of the long-term effect of progestational hormones in humans.