Steroids and human breast cancer

Estrogen receptor is present in the rat in target tissues, including mammary gland and hormone dependent mammary tumors, but is absent in non-target tissues and in many autonomous tumors. In human tissues, estrogen receptor behaves much like that of the rat. Its absence in a breast tumor specimen predicts the failure of hormone therapy, as shown by data collected from many sources, and this fact will be useful to clinicians in selecting therapy for metastatic breast cancer patients. The receptor is present, however, in a substantial number of nonresponsive tumors. These tumors may contain defects in the normal nuclear localization or action of the receptor-estrogen complex or even in the functions of other hormones which affect the mammary gland. These defects will have to be identified for a complete biochemical prognosis for endocrine therapy in breast cancer.