Low PI-RADS assessment category excludes extraprostatic extension (≥pT3a) of prostate cancer: a histology-validated study including 301 operated patients

Abstract

Objectives: To evaluate whether low PI-RADS v2 assessment categories are effective at excluding extraprostatic extension (EPE) of prostate cancer (≥pT3a PCa).

Methods: The local institutional ethics committee approved this retrospective analysis of 301 consecutive PCa patients. Patients were classified as low- or intermediate/high-risk based on clinical parameters and underwent pre-surgical multiparametric magnetic resonance imaging. A PI-RADS v2 assessment category and ESUR EPE score were assigned for each lesion by two readers working in consensus. Histopathologic analysis of the whole-mount radical prostatectomy specimen was the reference standard. Univariate and multivariate analyses were performed to evaluate the association of PI-RADS v2 assessment category with final histology ≥pT3a PCa.

Results: For a PI-RADS v2 assessment category threshold of 3, the overall performance for ruling out (sensitivity, negative predictive value, negative likelihood ratio) ≥pT3a PCa was 99%/98%/0.04 and was similar in both the low-risk (96%/97%/0.12; N = 137) and the intermediate/high-risk groups (100%/100%/0.0; N = 164). In univariate analysis, all clinical and tumor characteristics except age were significantly associated with ≥pT3a PCa. In multivariate analysis, PI-RADS v2 assessment categories ≤ 3 had a protective effect relative to categories 4 and 5. The inclusion of ESUR EPE score improved the AUC of ≥pT3a PCa prediction (from 0.73 to 0.86, p = 0.04 in the overall cohort). The impact of PI-RADS v2 assessment category is reflected in a nomogram derived on the basis of our cohort.

Conclusions: In our cohort, low PI-RADS v2 assessment categories of 3 or less confidently ruled out the presence of ≥pT3a PCa irrespective of clinical risk group.

Key points: • Our analysis of 301 mp-MRI and RARP specimens showed that the addition of PI-RADS v2 assessment categories to clinical parameters improves the exclusion of ≥pT3a (extraprostatic) prostate cancer. • PI-RADS v2 assessment categories of 1 to 3 are useful for excluding ≥pT3a prostate cancer with a NPV of 98%; such patients can be considered as candidates for less invasive approaches. • The ability to exclude ≥pT3a prostate cancer may improve confidence in choosing nerve-sparing surgery or in avoiding pelvic nodal dissections, and similarly for patients undergoing radiotherapy, in adopting short-course adjuvant hormonal therapy or foregoing prophylactic nodal irradiation.

Keywords: Magnetic resonance imaging; Nomogram; Prostate cancer.

Fig. 1

mp-MRI examination revealed an anterior, right lesion having a PI-RADS v2 score of 5 in a 66-year-old, clinically low-risk patient (cT1c, PSA 6.3, biopsy Gleason score 3 + 3) seen in (a) axial T2-weighted, (b) b1000 DWI, and (c) ADC map, where a pT3a, pathologic Gleason score 3 + 4 cancer was identified in (d) the histopathology specimen

Fig. 2

A right-sided, posterolateral lesion in a 65-year-old patient with a PI-RADS v2 score of 4 and EPE score of 2 at mp-MRI examination seen in axial (a) T2-weighted image, (b) subtracted DCE image, and (c) ADC map. At histology, the axial whole section of the apical portion of the prostate (d—upper right) without the posterolateral surgical margins sampled for intraoperative examination revealed a Gleason score 3 + 4 PCa. (d—lower left). In the intraoperative frozen section however, the PCa (hashed zone) was found to be pT3a, extending focally to the surgical margin (unhashed zone), including an extraprostatic site (*)

Fig. 3

Nomogram for the prediction of the risk of ≥pT3a PCa based on clinical risk group, ESUR EPE score, and PI-RADS v2 score. For each patient variable (Risk Group, ESUR EPE score, and PI-RADS v2), a vertical line is drawn from the value on the bar for that variable to the upper scale of points (dotted red lines show that low-risk group corresponds to 0 points in the upper bar, ESUR EPE score 4–5 corresponds to about 45 points, and PI-RADS v2 = 3 corresponds to 75 points). The sum of these three points is then located on the scale indicating the “Total Points” (here: 0 + 45 + 75 = 120 total points), and a vertical line is drawn downwards (green dotted line). Where this line intersects, the scale for Risk of ≥pT3a (%) gives the percentage risk of ≥pT3a PCa. Values outside the indicated bar should be read as risk < 10% (for Total Points < 100) or risk > 80% (for Total Points > 160), respectively. In the example above, a subject in the low-risk group, with a ESUR EPE score of 4–5 and PI-RADS v2 score of 3 has about 28% risk of ≥pT3a PCa