Role of progesterone receptors in breast cancer.

It has been demonstrated that progesterone receptors (PRs) are at least as valuable as estrogen receptors (ERs) for predicting outcome in breast cancer patients. Retrospective analysis indicates that the presence of PRs may be the second most critical factor, after the number of positive nodes, in predicting disease-free survival, with a correlation between length of survival and number of tumor PRs. The presence of PRs 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 the prognosis was worse for those patients whose tumors lost PR between assays.