Prostate-specific antigen is a new favorable prognostic indicator for women with breast cancer.

Prostate-specific antigen (PSA) is thought to be produced exclusively by prostatic epithelial cells and is currently used as a tumor marker of prostatic adenocarcinoma. We recently found that 30% of breast cancers contain PSA immunoreactivity (IR-PSA). To examine the prognostic value of PSA in female breast cancer, we measured IR-PSA in tumor cytosols of 174 breast cancer patients and classified the breast cancers as either PSA positive or PSA negative based on an IR-PSA cutoff level of 0.03 ng/mg. IR-PSA was present in 27% of the patients. IR-PSA presence was associated with early disease stage, small tumors, and estrogen receptor-positive tumors. We used the Cox proportional hazards regression model to analyze survival of patients in association with PSA status and found that patients with IR-PSA-positive tumors had a reduced risk for relapse and death in univariate analysis (P = 0.02 and 0.06, respectively) and a reduced risk for relapse in multivariate analysis (P = 0.03). Further analysis indicated that the effect of IR-PSA on relapse-free survival was evident in node-positive or estrogen receptor-negative patients. Our study suggests that IR-PSA is an independent favorable prognostic marker for breast cancer and may be used to identify a subgroup of estrogen receptor-negative and/or node-positive patients who have good prognoses.