progesterone receptor (PR)

A protein in some healthy and cancerous (malignant) cells that binds with progesterone.

A progesterone receptor assay (test) is used to find out if breast cancer cells have progesterone receptors, which will help doctors to decide on a treatment plan. If the cells have progesterone receptors, they are called progesterone receptor positive (PR+). If the cells don’t have progesterone receptors, they are called progesterone receptor negative (PR–).