Interpretation of Free Prostate Specific Antigen Clinical Research Studies for the Detection of Prostate Cancer

PURPOSE: We reviewed the use of percent free prostate specific antigen (PSA) to enhance specificity of PSA testing and aid in the discrimination of benign and malignant prostate disease. We present proposed percent free PSA cut points and probability factors, and discuss factors that are believed to affect study outcomes and conclusions. MATERIALS AND METHODS: We reviewed the literature with respect to PSA and free PSA with particular emphasis on clinical use of percent free PSA and factors that may affect study outcomes. RESULTS: Percent free PSA may increase the specificity of PSA testing without sacrificing the cancer detection rate. Differences in study designs and subject populations may account for the confusion in the current literature. Specific factors that may influence study outcomes include sample size, PSA range, age, race, digital rectal examination findings, prostate size, tumor size and pathology, as well as treatment history, sample collection and storage conditions, and the particular assays used to determine free and total PSA values. CONCLUSIONS: The use of percent free PSA to enhance the specificity of prostate cancer screening is thought to provide useful information to aid in the differentiation of benign and malignant prostate diseases. There is evidence to suggest a benefit cost advantage to a tailored biopsy approach based on percent free PSA. However, statistically valid multisite clinical trials that take into account influencing factors are needed to set assay specific cut points and probability determinations.