Multiparametric magnetic resonance imaging findings in men with low‐risk prostate cancer followed using active surveillance

Objective To assess the performance of multiparametric magnetic resonance imaging (MRI) in identifying pathological-index (path-index) lesions, defined as cancer present in the same prostate sextant in two separate surveillance biopsies, in men followed within an active surveillance (AS) programme for low-risk prostate cancer (CaP) with extended follow-up. Materials and Methods A total of 50 men, representing >215 person-years of follow-up in an AS programme, who were referred for prostate MRI were randomly chosen to have their images reviewed by a radiologist with expertise in prostate MRI, who was blinded to biopsy results. Index lesions on MRI were defined as a single suspicious lesion ≥10 mm or >2 lesions in a given prostate sextant. Lesions on MRI were considered suspicious if ≥2 abnormal parameters co-registered anatomically. Path-index lesions were defined as cancer present in a given prostate sextant on two separate biopsy sessions. Sensitivity and specificity were calculated to test the performance of MRI for identifying path-index lesions. Clinical and pathological features were compared between men with and without a MRI-index lesion. Results A total of 31 path-index and 13 MRI-index lesions were detected in 22 and 10 patients, respectively. Multiparametric MRI demonstrated excellent specificity and negative predictive value (0.974 and 0.897, respectively) for the detection of path-index lesions. Sensitivity (0.19) and positive predictive value (0.46) were considerably lower. Patients with an index lesion on MRI were younger and less likely to have met the ‘Epstein’ criteria for very low-risk CaP. Compared with men without an MRI lesion, a significant increase in biopsy reclassification was noted for men with a MRI lesion (40 vs 12.5%, P = 0.04). Conclusions A non-suspicious MRI was highly correlated with a lack of path-index lesions in an AS population. Multiparametric MRI may be useful in both the selection and monitoring of patients undergoing AS. Keywords: prostate cancer, surveillance, magnetic resonance imaging, sensitivity and specificity Introduction Widespread adoption of PSA screening has led to a significant downward risk migration in prostate cancer (CaP) over the past two decades [1]. Many of these cancers are diagnosed in older men and may have little impact on patient survival. As a result, active surveillance (AS) has emerged as an effective management option allowing many of these men to delay or possibly avoid definitive treatment and its associated side effects [2]. Despite careful patient selection, up to 35% of men in AS will experience biopsy reclassification during follow-up [3,4]. Non-invasive methods of cancer surveillance, including PSA and PSA kinetics assessments, are not considered reliable triggers for intervention in this population, and annual prostate biopsy is currently recommended by some for monitoring men undergoing AS [5]; however, serial prostate biopsies are associated with potentially serious infectious and quality-of-life sequelae [6,7]. Improved patient selection and less invasive methods of cancer surveillance are needed to improve the safety of AS in the management of low-risk CaP. Recently, MRI has shown promise in identifying men entering AS who are at risk of immediate pathological upgrading after repeat biopsy or radical prostatectomy (RP) [8,9], but the MRI characteristics of men within AS programmes who are at low risk of disease reclassification have not been fully described. Identification of these men through MRI has the potential to reduce a man’s exposure to serial prostate biopsies without compromising cancer surveillance. In the present study, we report our experience with multiparametric MRI in identifying pathological index (path-index) lesions, defined as cancer present in the same prostate sextant in two separate surveillance biopsies, in an AS cohort with extended follow-up.