Endocrine therapy for advanced carcinoma of the breast: relationship between the effect of tamoxifen upon concentrations of progesterone receptor and subsequent response to treatment.

In some cell lines and tumors of mammary origin, tamoxifen causes an increase of progesterone receptor (PR) as a result of its partial estrogen agonist activity. In this study we have assessed the effect of tamoxifen on PR in patients with advanced carcinoma of the breast in order to test if those with a rise in PR are more likely to respond to endocrine therapy. PR was measured before and a median of 13 days after treatment with tamoxifen in a group of 52 patients with either locally advanced (n = 28) or recurrent (n = 24) carcinoma of the breast. Controls were a group of patients with operable disease who had two biopsies with no intervening tamoxifen (n = 51) or with intervening tamoxifen (n = 58). In the test group PR was higher in the second biopsy than the first in 21 patients, and 19 of these responded to continued endocrine therapy (90%). In the remaining 31 patients PR was either lower in the second biopsy (n = 19) or was negative in both biopsies (n = 12), and 11 of the total of 31 patients (35%) responded to continued endocrine therapy. The prediction of response and time to progression was better when both biopsies were taken into account than either the first or the second alone. The prediction of survival was similar for the group selected by an increase in the second biopsy and the group with PR present in the second biopsy. The controls without tamoxifen showed a marked variation in the level of PR in the first and second biopsies, suggesting heterogeneity of PR across the tumors studied. However, the PR level was significantly higher in the second biopsy in the controls given tamoxifen and in the test group compared with those with no intervening treatment (p = 0.031). This study indicates that some effect of tamoxifen upon PR can be demonstrated in human mammary tumors in vivo and that, by taking a second biopsy for PR estimation during treatment with tamoxifen, a more precise indication of subsequent response is obtained. The value of a single estimation of PR before treatment on secondary deposits is limited, and if one biopsy only is performed, it is of greater predictive value if taken after a few days treatment with tamoxifen.