November 5, 2023
Progesterone receptor (PR) is a protein that allows a cell to respond to the actions of the hormone progesterone. After PR protein is made, it stays in a part of the cell called the nucleus. Progesterone hormone that enters the cell can change the behavior of the cell by activating PRs. Not all cells make PR. Cells that normally make this receptor are found in the breast, ovaries, uterus, and cervix. Some types of cancer including those of the breast, ovary, uterus, and cervix also make this receptor.
Immunohistochemistry (IHC) is a test pathologists perform to see PR-producing cells in a tissue sample. When combined with other immunohistochemical markers, this test allows pathologists to determine if the cells they are seeing under the microscope come from one of the organ systems that normally produces this protein. Cells that produce PR are typically described as ‘positive’ while those that do not produce the protein are described as ‘negative’. The percentage of cells producing the protein and the strength of the expression may also be reported.
Pathologists test all breast cancers to see if the tumour cells are making PR. This test is performed because tumour cells that make this receptor require the action of the progesterone hormone to help them grow. A patient with a PR-producing cancer is more likely to benefit from hormone-blocking medications. The response to the medication depends on the amount of progesterone receptor being produced. Tumours with higher levels of PR are more dependent on progesterone for growth and respond best to treatment.
This article was written by doctors to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.