Utility of PSA free-to-total ratio for clinically significant prostate cancer in men with a PSA level of <4 ng/mL.

Objective: To investigate the relationship between the prostate-specific antigen (PSA) free-to-total ratio (FTR) and International Society of Urological Pathology Grade Group ≥2, clinically significant prostate cancer (csPCa) in men with a low PSA level (≤4 ng/mL). Patients and Methods Data were obtained from the Prostate Cancer Prevention Trial. Patients with a PSA level of ≤4 ng/mL and who received a biopsy within a year of this PSA measurement were included. Associations between FTR and csPCa were investigated with logistic regression, adjusting for age and PSA, a re-scaled Brier score (index of predictive accuracy), and decision curve analysis.

Results: A total of 406 patients were analysed with 139 (34%) having csPCa and 204 (50%) having any grade PCa. For those with an FTR ≤0.15, 46% had csPCa, vs 22% for those with a ratio ≥0.20. In a regression model, the predicted probability of csPCa for a 60-year-old with a PSA of 3 ng/mL was 61% if the FTR was 0.05, falling to 18% if the FTR was 0.30. A clear negative relationship between increasing FTR and probability of csPCa was observed. A model containing FTR additional to PSA and age provides greater net benefit as per decision curve analysis and likely superior discrimination and calibration measured by a higher index of predictive accuracy.

Conclusions: In middle-aged men with a PSA level between 1.5 and 4 ng/mL but otherwise indicated for biopsy, a low FTR is associated with higher rates of csPCa. It should be utilised as an additional, readily available and inexpensive test to improve prediction of csPCa and aid in patient counselling.