c-H-ras-1 expression in 7,12-dimethyl benzanthracene-induced Balb/c mouse mammary hyperplasias and their tumors.

: Dimethylbenzanthracene (DMBA)-induced mouse mammary tumors characteristically contain an activated c-H-ras-1 gene with an A----T transversion in the 61st codon which is expressed as a rapidly migrating p21 c-H-ras. The role of the activated c-H-ras-1 locus in the initiation of mammary neoplasia was analysed by studying seven transplantable, DMBA-induced Balb/c premalignant mammary hyperplasias. The DNAs from these hyperplasias had no evidence of activation of the c-H-ras-1 gene. One of the fifteen tumors arising from untreated hyperplastic outgrowths had a 61st codon mutation. In contrast, 67% of the tumors developing in DMBA-treated hyperplasias had the characteristic 61 codon mutation. All of the tumors with the characteristic mutation expressed the corresponding rapid p21 c-H-ras. These data suggest that although c-H-ras-1 activation may play an important role in neoplastic progression, it had no definable role in the initiation or the maintenance of the mammary hyperplasias studied here.