This study enrolled all radical prostatectomies (n=70) operated on between January 1, 2015, to December 31, 2017. The inclusion criteria were pre-operative mpMRI performed at the author’s institution, either pre-biopsy or >1 year from biopsy, and available whole-mount histology. Patients with prior prostate cancer treatments were excluded. Each lesion was outlined on histology, with the high-grade components (Gleason 4 and 5) color-coded appropriately. Lesions on imaging were matched to histology (entire lesions and high-grade components) and measured at the same axial plane taking the mean of 2 readings.
Spearman’s rank correlation was used to compare mpMRI and histology. Bland-Altman plots were used to assess size discrepancies between imaging and histology, and evaluate the adequacy of mpMRI in measuring entire lesions or high-grade components. Per lesion analysis was performed, with statistical significance defined as p<0.05.
The mean age of patients was 65 (range 42-76), median PSA was 8.3 (0.45-41.2), and there were 122 MRI detected lesions. The sensitivity of mpMRI to detect cancer was 81%, with a false positive rate of 27%. Taking only true positives, mean lesion area was 108.9 mm2 on mpMRI and 107.9 mm2 on histology after shrinkage adjustment. The mean HG lesion area was 54.9 mm2. Comparing imaging with histology, rho=0.75 (95%CI 0.66-0.82, p<0.0001), and for imaging with HG cancers, rho=0.59 (95%CI 0.46-0.70, p<0.0001). On Bland-Altman test, the mean area difference was 1.98 mm2 (95% CI: -10.8 to 14.8, p=0.76), with a “sweet spot” range of 50 to 140 mm2(8 to 13 mm in diameter), where size discrepancies were ≤100 mm2 (5.6 mm in radial margin).
The scatter plot demonstrates a good correlation between MRI and pathology, regardless of measurement method
Because there are good size correlations between mpMRI and pathology, rigid standardization measurements are not imperative. Lesions up to 13 mm diameter are ideal for focal therapy; most high-grade cancers are safely ablated within 5-6 mm treatment margins of an entire lesion detected on mpMRI. Furthermore, according to Dr. Aslim, cancer missed by ablating lesions <13 mm is most likely low grade and less ominous. Ultimately, larger or multifocal lesions are likely better treated with zonal ablation or radical therapy.
Dr. Aslim concluded that there is a good correlation between lesion size on mpMRI and histology. They believe that the “sweet spot” may represent the ideal size range for focal ablation, with a safety margin of ~5.5 mm.
Presented by: Edwin J. Aslim, Singapore General Hospital, Department of Urology, Singapore
Written by: Zachary Klaassen, MD, MSc, Assistant Professor of Urology, Georgia Cancer Center, Augusta University - Medical College of Georgia, Twitter: @zklaassen_md at the 34th European Association of Urology (EAU 2019) #EAU19, conference in Barcelona, Spain, March 15-19, 2019.