Tamoxifen binding sites in human mammary cancers.

Tamoxifen binding sites (TBS) were measured using 3H-tamoxifen, the objective being to evaluate the relationships among TBS and hormone receptors and/or clinical and pathological characteristics in malignant tissues from 60 patients with mammary cancer. TBS were detected in most (96.7 per cent) cancers in the breast tissues, and the mean content and affinity were 569 fmol/mg X protein with Kd: 1.98 nM. There was no significant correlation between TBS and the estrogen receptor and/or progesterone receptor, with respect to positivity or content. However, there was a significant correlation between TBS and histological grading, thereby indicating the differentiation and the proliferative activity in this tissue. The content of TBS was significantly higher in the group with a high grade of malignancy. The TBS content significantly increased in parallel with the degree of malignancy, as related to tubule formation, nuclear pleomorphism and mitotic activity. On the other hand, there was no significant correlation between TBS and age, tumor size, lymph node status or clinical stage. These results suggest the possibility that TBS may be associated with differentiation and cell-proliferation in breast cancer tissues.