PGR and breast cancer: When protein extracts from partially purified fetal membranes, placenta, trophoblasts and decidua were compared with those from T47D breast cancer cells, using western blotting techniques with the PR antibodies that detected the cytoplasmic isoform in the immunohistochemistry studies (Figs 1 and 2; Table 2), several PR immunoreactive proteins were observed in T47D breast cancer cell extracts in line with previous studies [6,11,25,27,30], whereas the tissues at the fetal maternal interface revealed a major PR isoform with a relative molecular mass of ~60 kDa (Fig 5).