MRI IDs candidates for active surveillance of prostate cancer

Multiparametric MRI can help identify appropriate candidates for active surveillance of prostate cancer, performing on par with or better than existing clinical assessment scoring systems, and also improving the sensitivity of those systems, according to a study published online March 6 in Radiology.

Although active surveillance of prostate cancer is accepted as a treatment option for some men with smaller tumors of lower stage and grade, the accurate characterization of the disease is a concern when patients are committed to active surveillance. Existing systems are inconsistent, and random prostate biopsies may be prone to undersampling.

Baris Turkbey, MD, from the molecular imaging program at the National Cancer Institute, National Institutes of Health in Bethesda, Md., and colleagues designed the retrospective study to determine whether multiparametric MRI can help identify active surveillance candidates.

The researchers enrolled 133 patients (mean age, 59.3 years) with a mean PSA level of 6.73 ng/mL between January 2007 and August 2010. Two genitourinary radiologists evaluated T2-weighted images, apparent diffusion coefficient maps from diffusion-weighted (DW) MRI, MR spectroscopic images and dynamic contrast-enhanced MR images in consensus. They classified disease as low, moderate and high suspicion in each patient. In addition, one reader manually segmented the dominant tumor.

“Criteria for [active surveillance] at multiparametric MR imaging were having a dominant tumor smaller than 0.5 mL without extracapsular extension or seminal vesicle invasion  and a low imaging score (positive findings only on T2-weighted MR images and/or DW MR images or only on MR spectroscopy images or only on dynamic contrast-enhanced MR images).”

According to histopathologic criteria, 14 of 133 patients met established criteria for active surveillance. The sensitivity for of the D’Amico scoring system, Epstein criteria and CAPRA scoring system for predicting active surveillance candidates was 93 percent, 64 percent and 93 percent, respectively. Multiparametric MR delivered sensitivity of 93 percent.

The D’Amico scoring system led to misclassification of 30 percent of patients; however adding multiparametric MR to the method corrected 87 percent of misclassifications.

The Epstein criteria delivered a misclassification rate of 12 percent. “Although the Epstein criteria achieved an overall accuracy of 88 percent in stratifying [active surveillance versus active treatment] in our prostate cancer cohort, the criteria are inherently limited because of the undersampling of random biopsies, while incorporation of multiparametric MR imaging into the Epstein criteria improved the ability to stratify patients,” wrote Turkbey et al.

The CAPRA scoring system had a misclassification rate of 41 percent and sensitivity of 55 percent for stratification of patients to active treatment; the latter improved to 92 percent with the addition of multiparametric MR data.

MR depicted 126 of 133 dominant lesions. It failed to depict two tumors that proved to be dominant at histopathologic examination and substantially underestimated tumor volume in one patient. In seven patients, MR led to a correct estimate of tumor volume, but these low volume tumors were greater than Gleason grade 6.

The researchers referred to several shortcomings of the study. The small retrospective cohort study was conducted at a single institution, and included few patients eligible for active surveillance. Interpretation of MR images was subjective and binary; however, a standardized scoring system is in development.  

Turkbey and colleagues concluded by stressing the superiority of the multiparametric MR compared with existing scoring systems, and its capability to improve the accuracy of these systems when used together.