To elucidate the clinical relevance of our findings that Src is important for growth and signaling in the antiestrogen resistant T47D breast cancer cell lines, we evaluated the subcellular localization of total and phosphorylated Src by immunohistochemistry in tumors from 268 high-risk breast cancer patients, who have received tamoxifen as first-line adjuvant endocrine treatment. Here, SRC is linked to breast carcinoma.