Oral contraceptive-induced expression of prostate-specific antigen in the female breast

Prostate-specific antigen (PSA) is widely used as a tumor marker of prostatic adenocarcinoma. We recently found that 30% of breast tumors produce PSA and that PSA is a favorable prognostic marker in female breast cancer. We measured immunoreactive PSA in cytosolic extracts of normal breast tissue from eight women receiving no medication and one woman who was receiving no medication and one woman who was receiving the progestin-containing oral contraceptive Brevicon. None of the eight cytosolic extracts of normal breast tissue contained appreciable amounts of immunoreactive PSA. However, left and right breast tissues from the woman receiving Brevicon contained high levels of PSA. This immunoreactive species was shown to have a molecular weight identical to that of seminal PSA. Furthermore, reverse transcription of RNA and polymerase chain reaction amplification produced a 571-base pair cDNA that hybridized to a labeled cDNA PSA probe. Upon sequencing, the cDNA polymerase chain reaction product was found to have 100% homology with cDNA from prostatic tissue. PSA production by breast carcinoma cell lines was achieved after in vitro stimulation with norethindrone and ethinylestradiol. Our data suggest that PSA can no longer be regarded as a specific prostatic protein because it is produced by breast tumors with good prognosis and by normal breast tissue after steroid hormone stimulation.