The use of multiparametric MRI (mpMRI) of the prostate has exploded over the last 5 years, with some groups advocating for mpMRI screening prior to prostate biopsy. Dr. Rieter, discussed the available data on mpMRI that can help us assess the diagnostic accuracy of our diagnosis and its possible biological potential. MRI has been shown to have excellent accuracy in predicting clinically significant prostate cancer with a calculated sensitivity ranging from 80-90%. In a study comparing targeted MRI biopsies to standard (random) mapping prostate biopsies, mapping biopsies missed 31% of Gleason 7 and 42% of Gleason 8 tumors. The sensitivity of mpMRI to accurately diagnose clinically significant cancer increases with increasing lesion grading on MRI (PiRADS). In a study by Filson et al, 80% of targeted PiRADS 5 lesion were consistent with clinically significant cancers (Cancer 2016).
Recent studies have correlated PiRADS grade with prostatectomy upgrading and upstaging. A study by Hu et al, assessed the likelihood of upgrading and upstaging in men with very low risk prostate cancer who underwent mpMRI prior to radical prostatectomy. The study showed that the risk of upgrading and upstaging increased proportionally with the PiRADS grade. In a subsequent study, MRI grading was combined with Epstein criteria to increase its predictive ability. The addition of MRI grade to Epstein criteria increased the prediction accuracy to 95% in favorable for pathology and 98% for for unfavorable pathology.
There are several limitations associated with mpMRI of the prostate most notable is that MRI does not visualize all clinically significant tumors. Approximately 20% of index lesions are missed with MRI and 20% of targeted lesion are upgraded in the prostatectomy specimen. Tertiary Gleason 5 is commonly missed on MRI. This limitations by MRI can be bridge by the use of genomic testing and several trials are being conducted to assess the predictive accuracy the combined technologies.
There are two genetic tests available following the diagnosis of prostate cancer that can aid in determining the biological potential of the newly diagnosed low grade malignancy. OncotypeDx is a RNA based test that assesses the risk of unfavorable pathology on the prostatectomy specimen using a 17 gene panel. The Prolaris test by Miriad the other available test which assess the risk of death from prostate cancer using 31 cell cycle progression (ccp) genes, creating a ccp score. Both tests have been heavily studies for risk stratification of patients with low risk prostate cancer with very good predictive ability. A recent study by Salmasi et al, assessed the distribution of ccp scores of targeted biopsies when stratified by PiRADS grade. The study showed wide ccp score distribution along all grades, adding important biological information to PiRADS grading.
In conclusion, the introduction of mpMRI and genomic testing has allowed for greater risk stratification of patients diagnosed with low risk prostate cancer allowing us to further defined better candidates for active surveillance or active treatment.
Presented by: Robert Reiter, MD
Written By: Andres F. Correa, MD, Society of Urologic Oncology Fellow, Fox Chase Cancer Center, Philadelphia, PA
at the 2017 AUA Annual Meeting - May 12 - 16, 2017 – Boston, Massachusetts, USA