Enhancement by retinyl acetate of hormone-induced mammary tumorigenesis in female GR/A mice.

Feeding of retinyl acetate (82 mg/kg ration) for 13-16 weeks to estrone- and progesterone-treated nulliparous and multiparous inbred GR/A mice resulted in a substantial increase in the incidence of mammary carcinomas. Mammary carcinoma incidence in nulliparous control and retinoid-fed mice in experiment #1 was 22/65 (34%) and 37/65 (57%) (P less than 0.05), respectively; in experiment #2, 27/48 (56%) and 37/48 (77%) (P less than 0.05), respectively. Mammary carcinoma incidence in multiparous control and retinoid-fed mice in experiment #1 was 13/30 (43%) and 23/30 (77%) (P less than 0.05), respectively; in experiment #2, 19/19 (100%) and 19/19 (100%), respectively. The purported chemopreventive activities of retinyl acetate in murine mammary tumorigenesis were not demonstrated in this study; indeed, the vitamin A analog appeared to enhance this oncogenic process in the steroid hormone-treated GR mouse mammary cancer model.