4-(hydroxyphenyl)retinamide selectively inhibits the development and progression of ductal hyperplastic lesions and carcinoma in situ in mammary gland.

In most previous chemoprevention studies on inhibition of mammary carcinogenesis, the formation of palpable tumors has been used as an end-point. Little is known about whether chemopreventive agents may similarly or selectively suppress hyperplastic and premalignant stages of the neoplastic process. In this study, we evaluated the effect of 4-(hydroxyphenyl)retinamide (4-HPR) on the development and progression of hyperplastic lesions and carcinoma in situ (CIS) in the N-methyl-N-nitrosourea (MNU) mammary carcinogenesis model in rats. 4-HPR was used as the chemopreventive agent because of its proven inhibitory effect on both the early and late phases of mammary carcinogenesis. Treatment with 4-HPR (2.0 mM/kg diet), beginning 2 days after MNU administration and administered continuously for 10 weeks, suppressed all mammary gland lesions (hyperplasia, CIS and invasive carcinoma) in 35% of animals. In the remaining 65%, 4-HPR allowed the development of hyperplastic lesions, alone or combined with CIS, and/or invasive carcinomas (CA). 4-HPR also increased by 2-fold the ratio between CIS and CA (0.75 per animal in control versus 1.5 in 4-HPR-treated animals), suggesting that it may also suppress the transition of CIS into CA. 4-HPR, when administered beginning 4 weeks after MNU administration [when hyperplastic and premalignant (CIS) lesions are present in the mammary gland], inhibited the frequency of terminal end bud hyperplasia (TEBH) and CA but did not significantly suppress ductal hyperplasia, ductal alveolar hyperplasia, alveolar hyperplasia and CIS. In these animals, 4-HPR induced partial disintegration of mostly peripheral areas of lesions, including carcinomas. Taken together, our data indicate that 4-HPR selectively suppresses the development and progression of hyperplastic lesions and CIS in TEBs. Furthermore, it appears that, in addition to mammary carcinomas, TEBH and CIS could also be used as end-point biomarkers in breast cancer chemoprevention studies.