Renewed interest in the progesterone receptor in breast cancer

The progesterone receptor (PgR), a member of the nuclear receptor family, is a well-known oestrogen receptor (ER)-regulated gene that is expressed in over two-thirds of ER-positive (ER+) breast cancers ( Rakha et al, 2007 ). Progesterone receptor (PR) protein generally is assessed by immunohistochemistry at the time of diagnosis in primary breast cancers in most economically developed healthcare systems. PR is more highly expressed in the luminal A breast cancer subtype, and is associated with tumour grade, ER expression, Nottingham Prognostic Group and negative HER2 status in early breast cancer ( Arpino et al, 2005 ; Braun et al, 2013 ; Purdie et al, 2014 ). Multiple studies have demonstrated the improved prognosis of PR-positive (PR+) breast cancers ( Collet et al, 1996 ; Bardou et al, 2003 ; Viale et al, 2007 ; Blows et al, 2010 ; Van Belle et al, 2010 ; Purdie et al, 2014 ).