Transcriptomic Profile of Breast Tissue of Premenopausal Women Following Treatment with Progesterone Receptor Modulator: Secondary Outcomes of a Randomized Controlled Trial

Progesterone receptor antagonism is gaining attention due to progesterone's recognized role as a major mitogen in breast tissue. Limited but promising data suggest the potential efficacy of antiprogestins in breast cancer prevention. The present study presents secondary outcomes from a randomized controlled trial examining changes in breast mRNA expression following mifepristone treatment in healthy women. We analyzed 32 paired breast biopsies from 16 healthy premenopausal women at baseline and after two months of mifepristone treatment. In total, twenty-seven differentially expressed genes were identified, with enriched biological functions related to extracellular matrix remodeling. Notably, the altered gene signature induced by mifepristone in vivo was rather similar to the in vitro signature. Furthermore, this expression gene signature was associated with breast carcinogenesis and significantly correlated with progesterone receptor expression status in breast cancer, as validated in The Cancer Genome Atlas dataset using the R2 platform. The present study is the first to explore the breast transciptome following mifepristone treatment in healthy breast tissue in vivo, enhancing the understanding of progesterone receptor modulator and its potential protective effects against breast cancer by investigating its action in healthy breast tissue. Study subjects were randomized into two treatment groups, the randomization process is described in the original study. One group was treated with 50 mg mifepristone (one quarter of 200 mg Mifegyne®, Exelgyn) every other day for two months (56 days) starting on the first day of the menstrual cycle. The comparator group received B-vitamin tablets (TrioBe® Recip). For the purpose of the present study, only paired breast samples from the mifepristone treated group were analyzed.