Using proportions of free to total prostate-specific antigen, age, and total prostate-specific antigen to predict the probability of prostate cancer.

OBJECTIVES

This study was undertaken to define the probability of prostate cancer as a function of the proportion of free to total prostate-specific antigen (FTPSA), total PSA, and age for those patients with total PSA levels between 2.5 and 20.0 ng/mL.

METHODS

Prebiopsy serums were obtained from 428 untreated patients (165 malignant, 263 benign) who had undergone sextant six-core biopsy. Each patient had no prior history of prostate cancer and a prebiopsy total PSA value between 2.5 and 20.0 ng/mL. Total PSA levels were determined using the PA immunoassay performed on the TOSOH AIA-1200 automated immunoassay instrument. Free PSA levels were determined using a monoclonal-polyclonal antibody sandwich radioimmunoassay.

RESULTS

In men with total PSA values between 2.5 and 20.0 ng/mL, the FTPSA significantly differentiated between patients with benign and malignant histologic states. Log linear modeling indicated distinct differences in the risk for cancer as a function of FTPSA, total PSA, and age. The highest probability for cancer was observed in men greater than 70 years of age who had a FTPSA less than 7% and total PSA more than 10.0 ng/mL. Conversely, the lowest probability for cancer was observed in patients less than 60 years of age who had a FTPSA more than 25% and a total PSA less than 4 ng/mL.

CONCLUSIONS

The probability that prostate cancer will be found on biopsy has a marked gradient that is associated with age, total PSA, and FTPSA. The extreme ends of FTPSA of less than 7% and more than 25% are diagnostic for prostate cancer and benign prostatic disease, respectively.