Abstract
At the time of treatment in 1977 for primary breast cancer of all stages, the tumors of 270 women were examined for estrogen‐receptor (ER) content by iso‐electric focusing on polyacrylamide gel. The procedures for the initial and follow‐up examinations were standardized. Postoperative adjuvant radiotherapy or chemotherapy was given to pre‐ and postmenopausal women aged up to 70 years with nodal involvement. Adjuvant tamoxifen treatment (20 mg twice daily for 2 years) was given to one‐half of the postmenopausal patients aged 70 years or less, selected at random, and irrespective of any other adjuvant therapy. These forms of treatment appeared not to introduce bias into the results of the study. There was no correlation between the ER content and tumor spread. Symptom‐free survival during the follow‐up period was best for the patients with tumors with a high ER content, poorer for the patients with tumors of intermediate ER content and least favorable for patients with tumors having low ER content. (Ranges for high, intermediate and low levels: 2.18‐9.08, 0.13‐2.17 and 0‐0.12 fmoles/μg DNA). The differences between the survival curves were significant. For the 120 operable patients with nodal involvement there were also significant differences in recurrence‐free survival. The premenopausal patients in this group likewise showed a significant difference in survival with respect to ER content. For the operable patients with nodal involvement and poorly differentiated tumors there was also a difference in the survival rate depending on the ER content. In this study the ER content of breast cancer was shown to be a quantitative rather than a qualitative entity. The study confirms the independent prognostic importance of the ER content and points to its potential value as a stratification criterion in adjuvant therapy trials.