Effects of age at carcinogen administration and exposure as neonates to 17beta-estradiol on subsequent gland-pair distribution of murine mammary dysplasias.

The distribution of mammary dysplasias in 7,12-dimethylbenz[a]anthracene (DMBA)-treated BALB/c female mice differed with respect to the position of mammary gland pairs. The time of life when DMBA was given affected the incidence of lesions more than it did their distribution. Giving neonates injections of 49 mug 17beta-estradiol for the first 5 days of life resulted in increased numbers of dysplasia after DMBA administration at certain ages, but there was no consistent effect on gland-pair distribution of dysplasias at those ages. Possible reasons for differential gland-pair growth and occurrence of dysplasia are discussed.