We performed mammary carcinoma multiplicity studies with three mammary carcinoma-inducing treatments, namely 7,12-dimethylbenz(a)anthracene (DMBA) and N-nitroso-N-methylurea (NMU) carcinogenesis, and mammary ductal infusion of retrovirus expressing the activated HER2/neu oncogene. Here, ERBB2 is linked to breast carcinoma.