Use of IsoPSA with prostate MRI PIRADS score in biopsy decision making in patients with elevated PSA.

Abstract

388 Background: IsoPSA is prospectively validated to be superior to PSA and percent free PSA in predicting prostate cancer (PCa) as well as clinically significant prostate cancer. We sought to evaluate the use of IsoPSA in combination with prostate magnetic resonance imaging (MRI) and the prostate imaging reporting and data systems (PIRADS) on predicting either benign/indolent or csPCA at biopsy. Methods: This was a single center retrospective review of prospectively collected patient data that included all patients who underwent IsoPSA testing, preoperative prostate MRI and prostate biopsy from 2019-2021. Chi Squared analysis was used to assess for associations between a binary classification of low (<6) or elevated (>6) IsoPSA index, in combination with PIRADS scores in predicting either indolent/benign or csPCa at biopsy. Logistic regression was used to explore independent predictors of csPCa. Receiver Operating Curve (ROC) analysis was completed with areas under the curve (AUC) for IsoPSA and PIRADS scores, both alone and in combination. Predictive probabilities were assessed using combinations of IsoPSA thresholds and PIRADS scores. Results: 207 patients met inclusion criteria. Among patients with a negative MRI, low IsoPSA index was associated with a lower chance of csPCa compared to those with elevated IsoPSA (2% vs 15%, p<0.018). For those with a PIRADS 4-5 lesion, elevated IsoPSA index was associated with a higher chance of csPCa at biopsy compared to a low IsoPSA index (49% vs 19%, p=0.05). On multivariate analysis, elevated IsoPSA and PIRADS 4-5 were independent predictors of csPCa (p<0.001). Similarly, low IsoPSA index and negative MRI were independent predictors of benign/indolent disease at biopsy (p<0.001). Using predictive probabilities, the combination of PIRADS 4-5 with elevated IsoPSA was associated with the highest risk of csPCa (48%) and the highest AUC (0.83) for predicting csPCa. This AUC value was superior to either marker alone (0.76, 0.76) and total PSA alone (0.57) (p<0.001). Conclusions: The combination of elevated IsoPSA with adverse PIRADS score (4-5) is associated with a 48% predicted probability of csPCa at biopsy with an AUC of 0.83, which was more accurate than either marker alone. A low IsoPSA in combination with a negative MRI resulted in a 98% chance of benign/indolent disease at biopsy. These findings may prove useful for the practicing Urologist and may help guide discussions regarding the need for biopsy when interpreting various IsoPSA/PIRADS combinations. [Table: see text]