Stratifying risk of prostate cancer recurrence following external beam radiation therapy: Comparing prostate MRI with prostate biopsy pathology.

Background: In patients with clinically localized prostate cancer receiving external beam radiation therapy, studies have shown information from prostate biopsy cores can be predictive of clinical outcomes. Recent work from our institution compared several biopsy findings in low- and intermediate-risk patients and found a subset of patients who were more likely to fail treatment. This indicates patients in these groups may benefit from further risk stratification prior to initiation of therapy. Furthermore, findings on pre-treatment prostate MRI independently predict PSA relapse after external beam radiation therapy. Comparing MRI and pathological data may help to accurately further risk stratify patients. Our purpose is to determine if there is a correlation between the poor prognostic factors demonstrated on prostate biopsy cores and selected findings on prostate MRI. Methods: Intermediate risk prostate cancer patients with 1.5 and 3.0 Tesla MRI scans of the prostate performed from 2007-2011 were selected for a retrospective cohort study. Cases were reviewed by two body-trained radiologists who were blinded to clinical patient information. Reader consensus was obtained at the time of reading regarding presence of extracapsular extension, seminal vesicle invasion, and disease in each sextant by T2 and ADC imaging, including a dominant nodule. Results were analyzed for correlation between these findings on MRI and compared with results of prostate biopsy cores, including maximum involvement of any biopsy core (MIBC), percentage of cancer volume (PCV) and percent positive biopsy cores (PPBC). Results: The absolute presence of a dominant nodule on MRI was statistically significantly correlated with elevated PCV and PPBC applying the t-test for equality of means, with p-values of 0.019 and 0.006 respectively. PSA, Gleason score, and MIBC were not found to be correlated with dominant nodule on MRI. Conclusions: There is a strong positive correlation between MRI findings of a dominant nodule and prognostic biopsy findings of elevated PPBC and PCV.