Reviving the acid phosphatase test for prostate cancer.

Prostatic acid phosphatase (PAP) emerged as the world's first clinically useful tumor marker in the 1940s and 1950s. With the introduction of the prostate-specific antigen (PSA) test in the 1980s, which performed significantly better than PAP in terms of screening and monitoring response to treatment, PAP fell into disfavor. An increasing number of recent studies have identified PAP as a significant prognostic factor for patients with intermediate- and high-risk prostate cancer. PAP appears to be particularly valuable in predicting distant failure in higher-risk patients for whom high levels of local control are achieved with aggressive initial local treatment. As prostate cancer care becomes increasingly focused on identifying the minority of patients who would benefit from aggressive systemic therapy, a reevaluation of the potential contribution of the prostatic acid phosphatase test seems timely.