PGR and breast cancer: The demonstration that PR-C isoforms in the human breast cancer cell do not arise from proteolysis of larger PR-isoforms [13] but from two specific PR transcripts that originate from a 11.4 kb complex [5] and that specific PR mRNA transcripts are present in human fetal membranes and placenta that are not any of the other recognised PR isoforms (this study), strongly suggests that the 60 kDa isoform is generated through promoter specific transcription in extra-embryonic tissues.