Introduction

In the setting of active surveillance and focal therapy for prostate cancer (PCa), precise localization of the index lesion is crucial to ensure good oncological outcomes. Our objective was to assess the accuracy of multiparametric MRI (mp-MRI) for index lesion localization. _x000D_

Methods

We conducted a retrospective bi-centric study including 405 patients operated by radical prostatectomy from 2010 to 2015 and having been assessed preoperatively by mp-MRI in two national referral centres for PCa management._x000D_ Pre-operative mp-MRI sequences included T2-weighted, diffusion weighted, and dynamic contrast enhanced and were acquired from 1,5 (n=344) or 3 Tesla (n=61) with external phased array coils. The MRI index lesion was defined as the lesion with the highest PI-RADS score. The pathological index lesion was defined as the lesion with the greatest Gleason score. If there were multiple lesions with the same PI-RADS or Gleason score, the largest one was considered as the index lesion. A neighbouring method, dividing the prostate in 12 sectors, was applied to determine the concordance between mp-MRI findings and pathology reports for index lesion localization.

Results

Out of the 405 patients, 385 (95%) had an index lesion identified on the mp-MRI and 20 (5%) had a normal mp-MRI. On pathology reports, the Gleason score was 6 in 113 (28%), 7 in 252 (62%) and ≥ 8 in 40 (10%) of the patients. The index lesion diameter was greater than 10mm in 336 (83%) patients. For index lesion detection, mp-MRI had a sensitivity of 63%, a specificity of 67% and a positive predictive value of 66%. Increased sensitivity was obtained for larger tumors on mp-MRI (>10mm, 194/275; 71%) and greater biopsy Gleason score tumors (≥7, 147/202; 73%). _x000D_ In multivariate analysis, the detection of the index lesion by mp-MRI was significantly improved when the biopsy Gleason score was ≥ 7 (4+3) (p=0.001), the index lesion mp-MRI size was > 10mm (p<0.001) and the prostate weight was ≤ 50g (p=0.017).

Conclusions

In this contemporary assessment, mp-MRI failed to localize the index lesion in up to 40% of cases. Larger tumor sizes on mp-MRI and higher Gleason scores on biopsy cores were associated with significantly higher sensitivity of mp-MRI for index lesion localization.

Funding

none