Multiparametric MRI Identifies the Target
Meta-analyses and the prospective study PROMIS show that prostate cancer can be well localized and primarily classified by multiparametric MRI.
Multiparametric magnetic resonance imaging (mpMRI), a combination of T2-weighted imaging, diffusion-weighted imaging (DWI) and dynamic contrast-enhanced imaging (DCE), is a useful tool for prostate cancer detection. Heinz-Peter Schlemmer, Heidelberg University Hospital, Germany, went into the capabilities and limitations of the modality.
Sensitivities, specificities and limitations
The accuracy of mpMRI has been evaluated by a meta-analysis from deRooij et al. in 2014. “They found around 75% sensitivity and 88% specificity,” Schlemmer said. Negative predictive values ranged from 0.65 to 0.94.
The PROMIS study and the gold standard TRUS-biopsy: The prospective trial PROMIS proved mpMRI to have a statistically significantly higher sensitivity than TRUS-biopsy (93% vs. 48%) and negative predictive value (NPV 0.89 vs. 0.74). However, specificity of mpMRI was lower (41% vs. 96%) (Ahmed HU et al. 2017). “What is important, is that the sensitivity of mpMRI is higher than that of the gold standard,” Schlemmer said. “For staging, you can do TRUS biopsy.”
Missed cancers: The PROMIS trial also showed that around four percent of significant prostate cancers were missed by mpMRI. “The detection system simply has limits that we have to be aware of,” Schlemmer said. However, TRUS biopsy missed seven times more clinicallysignificant cancers than mpMRI.
A humane problem: Inter-reader variability
Reporting of prostate mpMRI is becoming increasingly standardized by using the Prostate Imaging Reporting And Data System (PI-RADS). However, Sonn GA et al. observed a considerable variability in PI-RADS score assignment and significant cancer yield across radiologists in mpMRI interpretation. “However, a high inter-reader variability was also observed among pathologists,” Schlemmer added.
Schlemmer recommended always working in a team and with other specialties. “Learn from the feedback you get. You will improve over time,” he promised.
Schlemmer underlined the importance of multiparametric MRI for prostate cancer detection. “It is the best modality despite its relatively low specificity,” he said. “Patients definitely benefit from it.”
Ahmed HU et al. PROMIS study group. Diagnostic accuracy of multi-parametric MRI and TRUS biopsy in prostate cancer (PROMIS): a paired validating confirmatory study. Lancet. 2017;389(10071):815-22.
Sonn GA et al. Prostate Magnetic Resonance Imaging Interpretation Varies Substantially Across Radiologists. Eur Urol Focus. 2017. pii: S2405-4569(17)30266-3.
de Rooij M et al. Accuracy of multiparametric MRI for prostate cancer detection: a meta-analysis. AJR Am J Roentgenol. 2014;202(2):343-51.