In the present study we used an animal model of hormone dependent breast cancer induced by 7,12-dimethylbenz(a)anthracene (DMBA) [19] to study the effect of tamoxifen therapy on expression levels of SRC-1, SRC-2/TIF-2, SRC-3/AIB1 and HER-2 in tumor tissue. This evidence concerns the gene SRC and neoplasm.