Nonprostatic sources of prostate-specific antigen

Until recently, prostate-specific antigen (PSA) was considered a highly specific marker of prostatic tissue. In this article, the authors summarize new knowledge documenting that PSA is expressed by many tissues and especially by the female breast. PSA can be produced by normal, hyperplastic, and cancerous breast tissue. PSA also is found in breast secretions such as breast milk and nipple aspirate fluid. The presence of PSA in breast tumors appears to be a predictor of good prognosis. The biologic function of PSA in nonprostatic tissues still is unknown. The presence of different molecular forms of PSA in the serum of women with breast cancer in comparison with healthy women may form the basis of a diagnostic test for breast cancer.