Occupied and unoccupied type II estrogen binding sites in human breast cancer.

Using a saturation analysis over a wide range of [3H]estradiol at two temperatures 4 and 22 degrees C we have determined unoccupied (4 degrees C) and total (22 degrees C) type II estrogen binding site (EBS) levels in individual cytosols of 100 patients with breast cancer (50 post and 50 premenopausal). Exchange was found to be complete after 18 h at 22 degrees C and receptor degradation was negligible during this treatment. Steroid specificity and affinity determined by Scatchard and Rosenthal plot analysis were not altered at 22 degrees C. Carcinomas presented a higher total type II REBS level as compared unfilled type II binding sites or the classical ER, independently of menopausal status, phase of the menstrual cycle or positivity of ER. On the other hand, unoccupied type II EBS level was strongly correlated to the concentration of type I ER, being higher on the post-menopausal group and older patients.