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 the nucleus of the cell. Progesterone hormone that enters the cell can change the behavior of the cell by activating the PR.
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.
Pathologists can perform a test called immunohistochemistry to see if a group of cells are making the progesterone receptor (PR). Cells that make this receptor will be called positive or reactive while those that do not will be called negative or non-reactive.
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 progesterone receptor 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.