Estrogen receptor levels and survival of breast cancer patients. A study on patients participating in randomized trials of adjuvant therapy.

A series of 1,022 patients taking part in clinical trials to compare postoperative radiation therapy with postoperative CMF chemotherapy, and postoperative tamoxifen with no adjuvant therapy, had their tumors analyzed for estrogen receptor content. Isoelectric focusing of the receptor in polyacrylamide gel was used for receptor assay and the results were related to tumor DNA content. The estrogen receptor content was significantly correlated to prolonged survival both for premenopausal and postmenopausal women. It was confirmed that postmenopausal women have increased median receptor values, and for this group values of more than approximately 0.3 fmol per microgram DNA were correlated to prolonged survival. For premenopausal women, a lower level of more than 0.1 fmol per microgram of DNA defined patients with prolonged survival. Lymph node involvement and receptor level were independent prognostic indicators. Patients randomized to tamoxifen or CMF tended to live longer as compared with control patients but this was not statistically significant. Moreover, there was no tendency for adjuvant tamoxifen to further increase the survival of patients with receptor-containing tumors as compared with control patients with similar receptor values.