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In a retrospective study we determined the relation between estrogen receptors and the response rate to cytotoxic chemotherapy in 70 patients with metastatic breast cancer. Thirty-four of 45 patients with low or absent estrogen-receptor values (less than 10 fmol per milligram of cytoplasmic protein) had objective responses to chemotherapy, whereas only three of 25 patients with higher values (greater than 10 fmol per milligram of cytoplasmic protein) responded (P less than 0.0001). There were no statistically significant differences between the two groups in age, menopausal status, disease-free interval, Karnofsky index or prior therapy. Differences in sites of involvement or type of chemotherapy did not account for the increased response rate in receptor-negative patients. We conclude that estrogen-receptor values are an important predictor of response to cytotoxic chemotherapy in metastatic breast cancer.

Other data reveal the important prognostic value of estrogen-receptor determinations in identifying patients at greater risk of relapse. The data of Drs. Legha et al. do not allow any conclusions on the effect of receptor status, as assessed (indirectly) by previous hormone responsiveness on response to chemotherapy. Dr. Panko has identified important potential problems with the study of Kiang et al. There is no question that some estrogen-receptor tumors can on substquent biopsies be estrogen-receptor positive; chemotherapy may enhance this selection of cells.