The progesterone receptor (PGR), also known as NR3C3 or nuclear receptor subfamily 3, group C, member 3, is an estrogen-regulated protein. It is activated by the steroid hormone progesterone. In humans, PR is encoded by a single PGR gene residing on chromosome 11q22, it has two main forms, PR-A and PR-B, that differ in their molecular weight. A third, lesser-known isoform, the PR-C, also exists. The PR-B is the positive regulator of the effects of progesterone, while PR-A and PR-C serve to antagonize the effects of PR-B.

It has been proposed that expression of PgR indicates a responsive estrogen receptor (ER) pathway. A number of studies have shown that PgR determination provides supplementary information to ER, both in predicting response to endocrine therapy and estimating survival. PgR has proved superior to ER as a prognostic indicator in some studies.