Role of progesterone receptors in breast cancer.

It has been demonstrated that progesterone receptor (PR) is at least as valuable as estrogen receptor (ER) for predicting the outcome in breast cancer patients. Retrospective analysis indicates that presence of PR may be the second most critical factor, after the number of positive nodes, in predicting for disease-free survival, with a correlation between length of survival and number of tumor PR. The presence of PR has been shown to be of value for predicting response in both early and advanced breast cancer patients. In studies of assay consistency, major discordance rates were minimal in simultaneous assays but extremely high in sequential assays of tumors that were PR positive in initial assay. The responsible factor was interim endocrine therapy, and it was subsequently determined that prognosis was worse for those patients whose tumors lost PR between assays.