Relationship between steroid receptors and response to endocrine therapy and cytotoxic chemotherapy in metastatic breast cancer.

The relationship between steroid receptor content and response of metastatic breast cancers to endocrine therapy and cytotoxic chemotherapy has been examined. In 54 advanced breast cancers treated with hormonal therapy, 20 of 29 (69%) ER+, PR+ and 3 of 14 (21%) ER+, PR- tumors responded. Of the nine tumors that lacked both ER and PR, 2 (22%) were hormonally responsive. Based on either the ER or PR content alone, 68% of the PR+ and 54% of the ER+ tumors responded to endocrine therapy. Thus, the addition of PR assay could improve the accuracy of ER assay in selecting a hormonally responsive breast cancer. In 29 advanced breast cancers treated with cytotoxic drugs, the presence of ER and/or PR in the tumors seemed to favor an objective response to cytotoxic chemotherapy. The response rate was about 67% regardless of whether the cancers were ER+ or PR+.