PR (progesterone receptor), with 933-amino acid protein (about 110kDa), a member of the steroid receptor superfamily, mediates the physiologic effects of progesterone, PR is mediated by two functionally different isoforms of the progesterone receptor, the full length PR-B and the short form PR-A, the PR-A and PR-B proteins are 94 kDa and 114 kDa respectively. that are equimolar in the normal breast but dysregulated in advanced disease is a prognostic marker in breast cancers irrespective of the patient’s progestational status Human progesterone.