Relationship of quantitative estrogen-receptor level and clinical response to cytotoxic chemotherapy in advanced breast cancer. An extramural analysis.

Three hundred twenty-four patients with advanced breast cancer from seven institutions whose x-rays and records had been externally reviewed for evidence of objective regression of disease were again reviewed, this time regarding their responses to chemotherapy in relationship to estrogen receptor (ER) levels. Higher levels of ER were found in older or postmenopausal women, in those with longer disease-free intervals or with osseous metastasis, and in women whose chemotherapy treatment was given later relative to first recurrence of disease. Response to chemotherapy in 60%, or 194 cases, was comparable to the response rate in other patients treated with the same drugs. Patients with ER levels greater than 3 fmoles/mg cytosol protein had a response rate of 67% and 58% of patients with ER less than 3 fmoles responded. Regimens containing Adriamycin (doxorubicin) and Cytoxan (cyclophosphamide) in combination appeared to give higher response rates. Addition of vincristine or prednisone did not improve response rates. The best response rate (88%) was in 16 patients who had ER levels in excess of 50 fmoles and received four or more drugs. There appeared to be a benefit from increased number of drugs and from quantitatively high ER levels. There is a discussion of the possible implication of these findings.