These models represent the major breast cancer subtypes found in humans, including triple-negative, basal-type lesions lacking BRCA1, HER2/ERBB2-positive tumors, as well as ERα-negative and ERα-positive, luminal-type cancers that originate in mice expressing mutant PTEN and prolactin in the mammary gland. This evidence concerns the gene ERBB2 and breast carcinoma.