Progesterone receptor (PR) is used along with ER as a prognostication marker in breast carcinoma. Expression is determined by percent positive and intensity (1+, 2+, 3+). PR is not as important of a prognostic marker compared to ER, but lower grade more differentiated tumors tend to show stronger expression of both ER and PR, and also have a better relative treatment outcome compared higher grade tumors.
A PR positive, ER negative, expression pattern should raise concern that either the slides were mislabeled, or the ER assay may not be performing properly. Most believe that ER expression is required for PR expression.
Outside of being used as a breast predictive marker, PR is not used too much in routine diagnostic surgical pathology.
Summary
- Nuclear Marker
- Stain is reported as PERCENT STAINING OF TUMOR CELLS and STAIN INTENSITY (1+, 2+, 3+)
- 1% or greater nuclear expression in tumor cells is considered positive
- PR expression is a prognostic marker, and not directly used for eligibility to receive a specific treatment
- PR expression without ER expression should raise significant concern that the ER and PR slides have been mixed up, or there is a problem with the ER assay. Many scientists believe that ER expression is required for PR expression.
Photomicrographs
References
Hammond ME, et. al. “ASCO-CAP Guideline Recommendations for IHC Testing of ER and PR in Breast Cancer”. Arch Pathol Lab Med-Vol. 134, June 2010.