Characteristically, the (MMTV)-ErbB2 transgenes recapitulating human breast carcinogenesis carry the viral MMTV-LTR promoter in order to ectopically express the ErbB2 oncoprotein in mammary epithelium (ErbB2 is amplified in up to 30% human breast cancers). The gene discussed is ERBB2; the disease is breast carcinoma.