PET/MRI Accurately Classifies Prostate Cancer Patients, Offers Potential to Avoid Unnecessary Biopsies

PET/MRI can improve diagnostic accuracy for prostate cancer patients and help avoid unnecessary biopsies, according to new research published in the April issue of The Journal of Nuclear Medicine. By applying the PRIMARY scoring system to PET/MRI results, researchers found that more than 80 percent of unnecessary biopsies could be avoided at the expense of missing one in eight clinically significant prostate cancer cases.

The Prostate Imaging Reporting and Data System (PI-RADS) is a five-point scale used to evaluate suspected prostate cancer on MR images. PI-RADS category 3, which presents an unclear suggestion of clinically significant prostate cancer, remains a diagnostic challenge. Although biopsy is recommended under the current guidelines, less than 20 percent of PI-RADS 3 lesions contain clinically significant prostate cancer.

“PI-RADS 3 lesions present a dilemma to both urologists and patients because immediate biopsy could be unnecessary; however, a monitoring strategy could lead to some missed diagnoses of clinically significant prostate cancer,” stated Hongqian Guo, MD, a urologist at Nanjing Drum Tower Hospital at the Affiliated Hospital of Nanjing University Medical School in Nanjing, China. “Hence, specifically ruling out clinically significant prostate cancer among PI-RADS 3 lesions has significant clinical implications.”

In this study, 56 men with PI-RADS 3 lesions underwent 68Ga-PSMA PET/MRI. The five-level PRIMARY system, which is based on a combination of 68Ga-PSMA pattern, localization, and intensity information, was used to report prostate 68Ga-PSMA PET/MRI findings. After imaging, all patients underwent prostate systematic biopsy in combination with targeted biopsy to determine clinically significant prostate cancer.

Among the 56 patients, clinically significant prostate cancer was detected in eight patients (14.3 percent) by biopsy. When a PRIMARY score of at least four was used to make a biopsy decision in men with PI-RADS 3 lesions, 40 of 48 (83.3 percent) participants could have avoided unnecessary biopsies, at the expense of missing 1 in 8 (12.5 percent) of clinically significant prostate cancer cases.

“By demonstrating the additive value of 68Ga-PSMA PET/MRI in classifying PI-RADS 3 lesions, this study provides new insight into the clinical indication for 68Ga-PSMA PET/MRI,” noted Guo. “In the future, PI-RADS 3 patients could be referred for 68Ga-PSMA PET/MRI before prostate biopsy.”

Figure 1. 68Ga-PSMA PET/MRI examples of PRIMARY scores. T2WI = T2-weighted image; PZ = peripheral zone; CZ = central zone.