PGR and breast cancer: M41 mRNA was shown to be produced by the carcinoma cells of breast cancer specimens using in situ hybridisation, and, using a PCR assay, M41 mRNA was found not to be statistically significantly correlated with the presence of oestrogen receptor, nor with the immunocytochemical detection of the oestrogen-responsive progesterone receptor (not shown) in a panel of carcinoma specimens.