Effect of short-term administration of N-(4-hydroxyphenyl)-all-trans-retinamide on chemically induced mammary tumors.

Mammary cancer was induced in 50-day-old Sprague-Dawley rats with either 25 mg/kg body weight of N-methyl-N-nitrosourea (MNU) or 10 mg/rat of dimethylbenz(a)anthracene (DMBA). The retinoid N-(4-hydroxyphenyl)-all-trans-retinamide (RAHA) was begun in the diet (2.0 mmol/kg diet) of MNU-induced rats at 21, 48, or 52 days of age, and at 21 or 60 days of age for DMBA-induced rats. RAHA was terminated 12-17 weeks postinduction, and the animals were sacrificed at 28 weeks postinduction. Significant inhibition of tumor incidence or multiplicity was found in only one group (rats fed RAHA beginning at 48 days of age). This was not considered sufficient evidence to conclude that short-term administration of RAHA altered mammary tumor development.