Prognostic significance of magnetic resonance imaging‐detected extraprostatic extension in localized prostate cancer

Background Magnetic resonance imaging (MRI) findings are not currently included in prostate cancer (PC) staging. Yet the presence of MRI‐detected extraprostatic extension (EPE) may indicate higher risk disease. The purpose of this study was to assess the prevalence of MRI‐EPE and prognostic ability in localized PC. Methods Patients with T1‐T2N0M0 PC diagnosed between 2000 and 2021 having a prostate MRI before definitive treatment were identified from the Veterans Affairs Prostate Data Core. MRI reports were assessed for major capsule abutment (MCA), extracapsular extension (ECE), seminal vesicle invasion (SVI), or organ invasion (OI). Any of these findings were considered EPE. Predictors of MRI‐detected EPE were assessed with a multivariable logistic regression. The impact of MRI findings on distant metastasis (DM) by multivariable Fine‐Gray competing‐risks regression was assessed. Results Overall, 2275 patients were included. Most pretreatment MRIs (85%) occurred after 2016. Approximately half the patients were Black. A total of 480 (21%) patients had palpable disease. Median follow‐up time was 5.1 years. The 5‐year cumulative incidence of metastasis was 4.8% (95% confidence interval [CI] 3.9%–5.7%). MRI indicated 468 (21%) patients had EPE: MCA (7%), ECE (10%), SVI (3%), and OI (1%). On multivariable analysis, the presence of MCA, ECE, SVI, and OI were each independently associated with worse DM. Findings of a digital rectal examination were also prognostic. Limitations included lack of centralized review of MRI images. Conclusion MRI‐detected EPE, including MCA, is common in localized PC and independently prognostic. MRI findings should be considered in the next iteration of PC staging.