Abstract

Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death in females worldwide. It is accepted that breast cancer is not a single disease, but instead constitutes a spectrum of tumor subtypes with distinct cellular origins, somatic changes, and etiologies. Molecular gene expression studies have divided breast cancer into several categories, i.e. basal-like, ErbB2 enriched, normal breast like (adipose tissue gene signature), luminal subtype A, luminal subtype B and claudin-low (Prat et al. 2010). Chances are that as our knowledge increases, each of these types will also be sub- classified. More than 66 % of breast carcinomas express estrogen receptor alpha (ERα) and respond to anti-estrogen therapies. Most of these ER + tumors also express progesterone receptors (PRs), the expression of which has been considered as a reliable marker of a functional ER. In this paper we will review the evidence suggesting that PRs are valid targets for breast cancer therapy. Experimental data suggest that both PR isoforms (A and B), have different roles in breast cancer cell growth, and antiprogestins have already been clinically used in patients that have failed to other therapies. We hypothesize that antiprogestin therapy may be suitable for patients with high levels of PR-A. This paper will go over the experimental evidence of our laboratory and others supporting the use of antiprogestins in selected breast cancer patients.