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.

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This work was supported by a Cancer Research Society, Inc. (Montreal, Canada) grant (E. P. D.) and the University Research Incentive Fund of the Province of Ontario (E. P. D.). D. K. is supported by an Associazione Italiana per la Ricerca sul Cancro fellowship.

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