Prostatic MRI before biopsy : a point of no way back

The PRECISION trial

The debate on to do or not to do a prostate MRI before biopsy is probably over. The PRECISION trial (1) is a multicenter study (25 centers, 11 countries) of 500 naïve biopsy men suspected of prostate cancer. All had a pre-biopsy MRI, performed by expert radiologists in each center. In case of suspicious MRI (PI- RADS≥3), the patients were randomized: one group had targeted biopsies only (by expert radiologists, each of them using the technique they are familiar with) and the other group had 12 systematic biopsies only.

The main objective was to compare the detection rate of significant cancer (Gleason score≥ 7), which was higher in the targeted biopsies group (38%) compared to the systematic biopsies group (26%, < 0.005). The secondary objective was to compare the detection rate of non- significant cancer between the two groups, which was lower in the group of targeted biopsies (< 0.001). MRI before biopsy and three targeted biopsies performed thus better than 12 systematic biopsies in patients with a suspicious MRI (figure 1*).

The basic oncological rule applied to the prostate

The trial shows that the prostate is now included in the general field of oncology where the rule is first to localize the lesion, then to use imaging to guide the biopsy. But this strategy requires a reliable detection of suspicious lesions on MRI using the PI-RADS score, available since 2016.

In the precision trial, the cancer detection rate was 83% for PIRADS 5, 60% for PIRADS 4 and 12% for PIRADS 3. However, assigning a PI-RADS score with a good reproducibility, remains a difficult exercise. In particular, a homogenous cancer detection rate of 12% for PI-RADS 3 lesions, observed in 25 centers from 11 different countries, implies a very high level of expertise of the involved radiologists to consistently assign a score 3. Indeed, the currently reported detection rate of significant cancer varies from 0 (2) to 66% (3) in score 3 lesions and from 21 (2) to 74% (3) in score 4 lesions, indicating a lack of reproducibility as shown by the only moderate to fair interreader concordance across centers (Kappa test: 0.39 (4) -0.49 (5) . The difficulty for differentiating a score 3 from a score 4 is related to the subjectivity of the PI-RADS category assessment in the peripheral zone (visual evaluation of the signal intensity of the diffusion) and in the transition zone (evaluation of the shape of a focal abnormality on the T2W sequence).

The consistent cancer detection rate in PIRADS 3 and 4 lesions observed in the PRECISION trial is an outstanding performance that reflects a high level of expertise requiring a long learning curve and a large volume of patients (300 per radiologist and per year in the study).

The need for a high accuracy Several prostate

MRI courses are organized in Europe, including ours, which help radiologists to become familiar with the PI-RADS and to be able to assign a probably benign score 3, corresponding to a score 2 and a suspicious score 3 comparable to a score 4.

By using all the available tools, some of which are not yet part of the PI-RADS, such as the use of very high computed b-values, and ADC metrics (+derivates), it becomes possible to get closer of a dichotomous approach (immediate biopsy versus delayed biopsy) in most cases, with the objective of discarding the PI-RADS 3 score, at least in the peripheral zone.

 

Caption Figure 1 : localizing value of an MRI before biopsy and targeted biopsies Suspicious focal abnormality in the right transition zone (arrow, a and b), visible on the T2 (a) and diffusion (b) image. The peripheral zone (ZP) is heterogeneous on the T2 image (a) but with no restrictive focus on the diffusion image (b). The four targeted biopsies (c) showed Gleason score 3 + 4 tumor. The 12 systematic biopsies were negative. The cancer location, very anterior on the specimen (arrow, b), explains that only MR-targeted biopsies were positive. Note the hyperplastic nodule hypointense and moderately restrictive (*).

 

References :

1. Kasivisvanathan V, Rannikko AS, Borghi M, Panebianco V, Mynderse LA, Vaarala MH, et al. MRI-Targeted or Standard Biopsy for Prostate-Cancer Diagnosis. N Engl J Med. 2018.

2. Mertan FV, Greer MD, Shih JH, George AK, Kongnyuy M, Muthigi A, et al. Prospective Evaluation of the Prostate Imaging Reporting and Data System Version 2 for Prostate Cancer Detection. J Urol. 2016;196(3):690-6.

3. Cash H, Maxeiner A, Stephan C, Fischer T, Durmus T, Holzmann J, et al. The detection of significant prostate cancer is correlated with the Prostate Imaging Reporting and Data System (PI- RADS) in MRI/transrectal ultrasound fusion biopsy. World J Urol. 2015.

4. Pierre T, Cornud F, Colleter L, Beuvon F, Foissac F, Delongchamps NB, et al. Diffusion- weighted imaging of the prostate: should we use quantitative metrics to better characterize focal lesions originating in the peripheral zone? Eur Radiol. 2017.

5. Rosenkrantz AB, Ginocchio LA, Cornfeld D, Froemming AT, Gupta RT, Turkbey B, et al. Interobserver Reproducibility of the PI-RADS Version 2 Lexicon: A Multicenter Study of Six Experienced Prostate Radiologists. Radiology. 2016;280:793-804.