Prospective development of a prostate cancer risk calculator in a racially diverse population: The Kaiser Permanente Prostate Cancer Risk Calculator

Purpose: To prospectively develop a prostate cancer (CaP) risk calculator in a racially diverse population.

Materials and methods: All patients referred for prostate biopsy due to an elevated prostate-specific antigen or abnormal digital rectal exam in a 19-months period at Kaiser Permanente Northern California underwent a standardized systematic, ultrasound-guided biopsy scheme (14-cores for initial biopsy, 18-20 cores for repeat biopsy). All pertinent clinical variables were prospectively collected. The highest Gleason score for each patient was recorded for all positive biopsies. We used a split sample design to develop and validate 3 multivariable prediction models using multinomial logistic regression with the least absolute shrinkage and selection operator. All models included these core variables: age, race, prostate-specific antigen, prior biopsy status, body mass index, and family history of CaP. Model 1 included only the core variables, Model 2 added digital rectal exam, and Model 3 added digital rectal exam and prostate volume. We considered 3 outcomes: high-grade disease (Gleason score ≥7), low-grade disease (Gleason score = 6), and no cancer. Predictive discrimination was quantified using the c-statistic.

Results: Complete data were available for 2,967 patients. Cancer was found in 50% of patients: of these, 58% were Gleason score ≥7 and 42% were low grade. Compared to Caucasians, African Americans were at a higher risk while Asians and Hispanics were at a lower risk for overall and high-grade cancer detection. The number of prior negative biopsies was also protective for these outcomes. The c-statistics for Model 1, 2, and 3 to predict high-grade disease vs. low-grade or no cancer were 0.76, 0.79, and 0.85, respectively. The c-statistics for Model 1, 2, and 3 to predict any CaP vs. no cancer were 0.69, 0.70, and 0.79, respectively. All models were well calibrated for all outcomes.

Conclusions: In men with elevated PSA levels, our calculator provides useful information that may enhance the shared decision-making process regarding the need for biopsy.