56 Background: Multiparametric MRI has emerged as a popular imaging modality to localize prostate cancer. Nevertheless, interpretation of MRI is subjective, with concerns for false positives, particularly in the transitional zone (TZ), where hyperplastic changes may be confused for suspicion of cancer. We analyzed a prospective cohort of men undergoing MRI-US fusion biopsy and compared cancer detection rate between lesions seen in the peripheral zone (PZ) and the TZ. Methods: 133 men with elevated PSA or positive DRE underwent MRI-US fusion biopsy with average of 2 cores taken per target for the detection of prostate cancer between October 2014 and July 2015. Each targeted lesion in the PZ and TZ was previously classified by radiologists according to the MRI PI-RADS score and grouped according to their level of suspicion as probably benign (1-2), indeterminate (3) or probably malignant (4-5). Histopathology from targeted cores were categorized as no cancer, non-significant cancer (Gleason 6) and significant cancer (Gleason ≥ 7). We compared the cancer detection rates between lesions in PZ and TZ lesions, based on PI-RADS score. Results: We identified 143 lesions in the PZ and 82 lesions in the TZ. Among lesions found in the TZ, 57.3% were reported as probably malignant, compared to 44.7% of lesions seen in the PZ. Cancer was diagnosed in 23% of the lesions in the PZ, compared to only in 9.7% in the TZ (p<0.01). With respect to significant cancer there was a trend towards higher detection of significant cancer in the PZ (13.29% vs. 6.10% p=0.12) compared to TZ. Furthermore, lesions in the PZ with a PI-RADS score > 4 were associated with a three-fold increase in the odds of detecting cancer compared to lesions with PI-RADS < 4 (OR 3.08; CI 95% 1.29 – 7.31, p<0.011), whereas in the TZ there was no increased risk of cancer with higher PI-RADS scores (OR 1.0 CI 95% 0.20 – 4.84, p<1.0). Conclusions: To our knowledge this is the first study to address a concern regarding an increased likelihood of false positives when reporting the presence and aggressiveness of cancer in the TZ versus the PZ. This may lead to unnecessary biopsies in men undergoing MRI of the prostate.
MP21-16 3T MULTI-PARAMETRIC MRI PERFORMANCE IN PROSTATE CANCER DETECTION: PERIPHERAL ZONE TUMORS VS. TRANSITIONAL ZONE