Prostate tumors are often undersized in MR imaging and can be undertreated as a result, say researchers at UCLA Jonsson Comprehensive Cancer Center.

“Multiparametric magnetic resonance imaging frequently underestimates pathological tumor size and the degree of underestimation increases with smaller radiologic tumor size and lower PI-RADSv2 scores. Therefore, a larger ablation margin may be required for smaller tumors and lesions with lower PI-RADSv2 scores,” wrote the authors in their study.

Underestimation of tumor size can deter successful prostate tumor treatment, which requires both the MR size measurement and PI-RADS score to be accurate so that physicians can precisely determine where the tumor ends and where healthy, surrounding tissue begins.

Researchers evaluated 461 consecutive lesions in 441 men. Mean radiologic tumor size was 1.57 cm and pathological tumor size was 2.37 cm. They found that radiologic tumor size consistently underestimated the pathological tumor size regardless of the preoperative covariates.

In addition, the degree of underestimation increased with smaller radiologic tumor size and lower PI-RADSv2 scores. Pathological tumor size was significantly larger for biopsy Gleason Grade Group 5 compared to GG1, PI-RADSv2 5 lesions compared to PI-RADSv2 4, and higher prostate specific antigen density. Correlations between radiologic tumor size and pathological tumor size were generally lower, based on biopsy GG and radiologic covariates, with correlation coefficients ranging from 0.1 to 0.65.

“Improving the ability to better predict ablation margins will allow for more successful treatments for men with prostate cancer and can help reduce the morbidity of prostate cancer treatment,” wrote the authors.

The findings were published in the Journal of Urology.