Significance of quantitative assessment of estrogen receptors for endocrine therapy in advanced breast cancer.

The predictive significance of quantitative assessment of estrogen receptors in tumor tissue was analyzed in women with advanced breast carcinoma. Receptor concentration was measured by the 3H-estradiol binding capacity of the cytosol fraction of biopsies taken before initiation of the treatment. The E. O. R. T. C. criteria for the assessment of the patients' response were used. In a total of 34 assessments, 25 biopsies contained receptors; the remaining ones were negative. Objective remission to various endocrine therapies was recorded in only eight of the receptor-positive patients. Responses occurred along the whole scale of receptor concentrations with an apparent crowding in the region of the higher values. Linear logistic regression analysis revealed that among 12 variables of known prognostic value, receptor concentration was the most significant in relation to therapeutic response. Other significant variables were bone involvement and age. Computations yielded formulas that are presented in graph form and provide an estimate of the probability of a given patient to respond to endocrine treatments. On the other hand, the results suggest that all patients are possibly hormone dependent, although to variable degrees. The latter concept has very definite therapeutic implications.