Pathologic prostate tumor size is often larger than indicated on 3 Tesla multiparametric magnetic resonance imaging (3T mpMRI), a finding that has clinical implications for use of such imaging for focal therapy.
A team led by Aydin Pooli, MD, of the Institute of Urologic Oncology at the University of California, Los Angeles, compared radiologic and pathologic results for 461 lesions (in 441 men) who underwent preoperative 3T mpMRI followed by radical prostatectomy. Results published in the Journal of Urology showed that mean radiologic tumor size was significantly smaller than pathologic tumor size: 1.57 vs 2.37 cm, respectively. As radiologic tumor size and PI-RADS version 2 score decreased, the degree of inaccuracy increased.
Radiologic and pathologic tumor size had low correlation coefficients of 0.1 to 0.65 when Gleason grade group (GG) and PI-RADSv2 score were taken into account.
Mean pathologic tumor size was a significant 0.37 cm and 0.26 cm larger for biopsy GG 5 vs GG1 lesions and PI-RADsv2 5 vs 4 lesions, respectively. In addition, mean pathologic tumor size increased by a significant 0.17 cm for each 2-fold increase in PSA density.
“Our study suggests that when considering management options for [prostate cancer], greater caution must be applied for smaller tumors on mpMRI and lower PI-RADSv2 scores given more significant size underestimation for such tumors,” Dr Pooli’s team stated. They highlighted the need for additional tools to determine tumor treatment margins when considering focal ablation therapies.
In an accompanying editorial, Joseph L. Chin, MD, of Western University, London Ontario, Canada, lauded the investigators’ efforts, but cautioned that “urologists performing focal therapy cannot assume they can fully compensate for any radiologic underestimation of tumor size with literal margin expansion of the magnetic resonance target (by the amounts reported in this paper).”
Pooli A, Johnson DC, Shirk J, et al. Predicting pathological tumor size in prostate cancer based on multiparametric prostate magnetic resonance imaging and preoperative findings. J Urol. 2021:205:444-451. doi:10.1097/JU.0000000000001389
Chin JL. Editorial Comment. J Urol. 2021;205:451. doi:10.1097/JU.0000000000001389.01