Endocrine therapy for advanced carcinoma of the breast: effect of tumor heterogeneity and site of biopsy on the predictive value of progesterone receptor estimations.

This study was carried out to assess the influence of site of biopsy and tumor heterogeneity upon the value of progesterone receptor (PR) measurements for prediction of response of patients with advanced carcinoma of the breast to tamoxifen or ovarian ablation. One hundred eighty-one assessable patients were studied. Sixty-nine % of responders and 31% of nonresponders were PR positive. The times to progression and survival were not significantly different for responders whether they were receptor positive or receptor negative. PR was measured on operable primary tumors (97), inoperable primary tumors (59), and secondary deposits (69). The proportion of responders who had PR-positive biopsies from these sites was 59%, 88%, and 61%, respectively, and the proportion of PR-positive nonresponders was 30%, 27%, and 42%, respectively. Ten to 12 separate PR measurements were made on seven tumors, and in four of them, there were PR-positive and PR-negative areas which could account for false positive and false negative results. We conclude that the optimum prediction of response was seen when the biopsy was performed on inoperable primary tumors. Errors in prediction of response at this site were, in part, explained by within-tumor heterogeneity of PR; the greater errors in prediction when measurements were made on operable primary tumors or on secondary deposits are presumed to be related to the additional effects of change in receptor status with time and between-tumor-site heterogeneity, respectively.