Simplified Extraprostatic Extension grade (sEPE grade): a new predictive score for MRI assessment of extraprostatic tumor extension

Objectives: (i) to assess the reproducibility and predictive value of a simplified score for evaluating extraprostatic tumor extension (sEPE grade). (ii) To test the predictive value of the simplified score on site specific tumor location namely anterior or posterior zone. Methods: Sixty-five patients (mean age ± SD, 67 years±6.3) with prostate cancer treated by radical prostatectomy, who underwent 1.5 Tesla multiparametric magnetic resonance imaging (mpMRI) within six months before surgery, were included. Concerning tumor location: in 18 patients’ prostate cancer was in the anterior zone and in 42 patients was in the posterior zone. sEPE grade was derived from mpMRI metrics: curvilinear contact length >15 mm (CCL), and capsular bulging/irregularity. The diameter of the index lesion (dIL) was also measured. Evaluations were independently performed by seven radiologists, and inter-reader agreement was tested by weighted Cohen K coefficient. A nested (two levels) Monte Carlo cross-validation was used. The best cut-off value for dIL was selected by means of the Youden J index to classify values into a binary variable termed dIL*. Logistic regression models based on sEPE grade, dIL* and clinical scores were used to predict pathologic EPE. Results on validation set were assessed by the main metrics of the Receiver Operating Characteristics Curve (ROC). Decision curve analysis (DCA) was performed. Based on our findings we defined and tested an alternative sEPE grade formulation. Afterwards, the diagnostic performance of the alternative sEPE grade formulation was assessed on site specific tumor location. Results: Pathologic EPE was identified in 31/65 (48%) patients. The average weighted kappa coefficient was 0.65 (95%C.I. 0.51-0.79), 0.66 (95%C.I. 0.48-0.84), 0. 67 (95%C.I. 0.50-0.84), and 0.43 (95%C.I. 0.22-0.63) for sEPE grading, CLL ≥15 mm, dIL* and capsular bulging/irregularity, respectively. The highest diagnostic yield in predicting EPE was obtained by combining both sEPE grade and dIL*(ROC-AUC 0.81). sEPE showed the highest AUC of 88% for depicting EPE of the anterior zone lesions. Conclusions: The sEPE grade is reproducible and, when combined with dIL*, effectively predicts extraprostatic tumor extension, especially for anterior zone lesions.