PGR and breast neoplasm: In order to determine whether changes in D6-PR variant expression could occur during tumorigenesis, its expression was investigated by reverse transcription and polymerase chain reaction in ten normal reduction mammoplasty samples, nine breast tumours with high PR levels (> 100 fmol mg−1 protein) and eight breast tumours with low PR levels (< 15 fmol mg−1 protein), as determined by ligand binding assay.