Magnetic resonance-invisible versus magnetic resonance-visible prostate cancer in active surveillance: a preliminary report on disease outcomes.

OBJECTIVE To assess the association between magnetic resonance (MR) appearance of prostate cancer on a baseline multiparametric prostate (MP) MR imaging (MRI) and biopsy outcome in men with favorable-risk prostate cancer managed with active surveillance (AS). MATERIALS AND METHODS Ninety-six consecutive men (mean age, 67.8 years) who had a baseline MP MRI within 1 year of AS enrollment were included in the study. MP MRI results were analyzed to identify men with MR-invisible tumor defined as no signal abnormality on T2-weighted images, no focal restricted diffusion, and no perfusion abnormality on dynamic contrast-enhanced images. Patients with (n = 84) or without (n = 12) MR-visible tumor were compared and the impact of MR-invisibility of tumor on the risk of adverse biopsy pathology based on the Epstein criteria was investigated with a median follow-up of 23 months. RESULTS Adverse biopsy pathology occurred in 36.5% (35 of 96) of patients. There was no significant difference in the fulfillment of AS criteria at enrollment, prostate-specific antigen level or density, prostate volume, and number of biopsies (total or after MRI) between the 2 groups of patients. A total of 8.3% (1 of 12) of men with MR-invisible tumor had adverse biopsy pathology as compared with 40.5% (34 of 84) of men with MR-visible tumors. The MR-invisibility of tumor was associated with a lower risk of adverse biopsy pathology (crude relative risk = 0.35; 95% confidence interval, 0.10-1.25; prostate-specific antigen density-adjusted relative risk = 0.21; 95% confidence interval, 0.03-1.32). CONCLUSION The MR-invisibility of tumor on MP MRI could be of prognostic significance in monitoring men in AS with potential benefit of tailoring the frequency of surveillance biopsies and reducing the number of unnecessary biopsies.