A high-tumor-incidence subline of the D1 mouse mammary hyperplastic outgrowth line: effect of carcinogens.

Mammary tumorigenesis in some mouse strains is characterized by the appearance of a preneoplastic lesion, the hyperplastic alveolar nodule (HAN). The biology of the HAN has been characterized primarily through the study of stable outgrowth lines of serially transplanted HAN. One outgrowth line, Dl, which was developed and carried in female BALB/c mice, has been described as a low-tumor-incidence line that does not express murine mammary tumor virus (MuMTV) and is susceptible to hormonal, chemical, and viral carcinogens. In this report, a high-tumor-incidence subline of Dl, Dl/UCD, is described. Although Dl/UCD, like Dl, is susceptible to the chemical carcinogen 7,12-dimethylbenz[a]anthracene, an increase in tumor incidence was not observed when Dl/UCD outgrowth was exposed to hormones by means of pituitary isografts. Unlike Dl, Dl/UCD is refractory to the carcinogenic action of MuMTV. Both Dl and the Dl/UCD subline contained the endogenous MuMTV provirus but did not contain exogenous MuMTV provirus sequences. MuMTV antigen was not detected in Dl/UCD outgrowths or tumors. RNA hybridizable to MuMTV complementary DNA was detected in some Dl/UCD outgrowths and tumors but did not appear to correlate with tumorigenesis.