Validating multiparametric MRI for diagnosis and monitoring of prostate cancer in patients for active surveillance.

Purpose: To compare multiparametric magnetic resonance imaging (mpMRI) with transrectal ultrasound-guided prostate biopsy (TRUS-bx) for the diagnosis and monitoring of small-volume prostate cancer (PCa) in patients on active surveillance (AS).

Methods: In a retrospective cross-sectional validation study, 100 patients on AS for PCa underwent a systematic 12-core TRUS-bx (the gold standard) as well as mpMRI, on either a 1.5 or 3 Tesla scanner (32 and 68 patients, respectively). Three pathologists reported biopsy histology separately. A single, experienced radiologist scored mpMRI scans using the PI-RADS system. We compared left- and right-sided PI-RADS scores of the peripheral zone with TRUS-bx results of the relevant prostate lobe. We then estimated the specificity and sensitivity of mpMRI in diagnosing low-grade low-risk PCa in our AS cohort.

Results: The sensitivity of mpMRI was 37% (95% CI 28-47%) and specificity was 85% (CI 76-92%) for cancer. The negative predictive value was 51% (CI 44-60%), and the positive predictive value was 76% (CI 62-87%). The positive and negative likelihood ratios were 2.5 and 0.7, respectively.

Conclusion: Because of its low specificity and low negative predictive value, mpMRI is not suitable for diagnosing low-grade small-volume PCa. However, because of a specificity of 85% and a negative likelihood ratio of 0.7, mpMRI may be useful for follow-up of previously TRUS-bx diagnosed patients who are on AS.