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Study: PET/MRI May Prevent Up to 83 Percent of Unnecessary Biopsies in Men with PI-RADS 3 Lesions


For men with PI-RADS 3 lesions, PRIMARY scores of 4-5 with PET/MRI had a sensitivity rate of 87.5 percent for clinically significant prostate cancer, according to newly published research.

Can 68Ga-PSMA PET/MRI enhance risk stratification for PI-RADS 3 lesions?

In a new prospective study, recently published in the Journal of Nuclear Medicine, researchers reviewed data from 56 men who had 68Ga-prostate-specific membrane antigen (PSMA) positron emission tomography (PET)/magnetic resonance imaging (MRI) and prostate systematic biopsies. The study participants were previously diagnosed with PI-RADS 3 lesions based on multiparametric MRI (mpMRI) findings, according to the study.1

Using a recently described five-level PRIMARY scale to review the PET/MRI findings, the researchers noted no positive cases among study participants with PRIMARY scores of 1 (no pattern with low-grade activity) and 2 (diffuse transition zone or symmetric central zone pattern). Out of 16 participants with a PRIMARY score of 3 (focal transition zone pattern), there was one diagnosis of clinically significant prostate cancer (csPCa), according to the study authors.1,2

Out of 13 men with a PRIMARY score of 4 (focal peripheral zone pattern with no minimal intensity), five had csPCa. The researchers also noted that both patients with a PRIMARY score of 5 (any pattern with intense uptake and a SUVmax > 12) were diagnosed with csPCa.1

Study: PET/MRI May Prevent Up to 83 Percent of Unnecessary Biopsies in Men with PI-RADS 3 Lesions

Here one can see PET, T2-weighted MRI and 68Ga-PSMA PET/MRI images reflecting a PRIMARY score of 4 for focal activity involving the peripheral zone (top images) and a PRIMARY score of 5 showing intense uptake and a SUVmax > 12. (Images courtesy of the Journal of Nuclear Medicine.)

The study authors found that utilizing the PRIMARY scoring system with 68Ga-PSMA PET/MRU had a 91 percent AUC for detecting csPCa in men with PI-RADS 3 lesions. Using a threshold of PRIMARY 4 and 5 scores, the researchers noted an 87.5 percent sensitivity rate, an 83.3 percent specificity rate and a 97.5 percent negative predictive value (NPV).1

“Adding a PRIMARY score of at least 4 into the biopsy decision could avoid 83.3% (40/48) (of) unnecessary biopsies at the expense of missing 12.5% (1/8) of csPCa cases. … To the best of our knowledge, this is the first prospective study to show the value of 68Ga-PSMA PET/MRI in classifying PI-RADS 3 lesions and to avoid unnecessary biopsy,” wrote lead study author Jingyan Shi, M.D., who is affiliated with the Department of Urology at Nanjing Drum Tower Hospital and the Affiliated Hospital of Medical School at Nanjing University in Nanjing, China, and colleagues.

Three Key Takeaways

  1. Improved risk stratification. Incorporating 68Ga-PSMA PET/MRI with the PRIMARY scoring system enhances risk stratification for PI-RADS 3 lesions. Specifically, using a threshold of PRIMARY scores 4 and 5 significantly improves specificity (83.3 percent) while maintaining high sensitivity (87.5 percent) for detecting clinically significant prostate cancer (csPCa).
  2. Reduced unnecessary biopsies. Integrating a PRIMARY score of at least 4 into the biopsy decision-making process could potentially reduce unnecessary biopsies by 83.3 percent. This reduction in unnecessary biopsies comes with a minor trade-off of missing 12.5 percent of csPCa cases. This approach highlights the potential to optimize patient care by avoiding invasive procedures when they are not warranted.
  3. Value of 68Ga-PSMA PET/MRI. This study suggests that 68Ga-PSMA PET/MRI has a significant clinical value in classifying PI-RADS 3 lesions and aiding in biopsy decision-making. The combination of mpMRI and 68Ga-PSMA PET offers improved specificity over mpMRI alone, potentially leading to more accurate detection and management of csPCa.

While acknowledging the well-known sensitivity of mpMRI for csPCA and the improved specificity offered by 68Ga-PSMA PET, the researchers suggested that use of the PRIMARY scoring system with the combination of 68Ga-PSMA PET/MRI could enhance csPCa detection.

“ … Compared with a threshold of (PRIMARY score) 3 and a cutoff of (PRIMARY score) 4, specificity was improved significantly from 52.08% to 83.33%, while preserving a high level of sensitivity (decreasing from 100% to 87.5%),” maintained Shi and colleagues.

(Editor’s note: For related content, see “ECR Study Examines Key Predictive Factors for Metastasis in Patients with High-Risk Prostate Cancer,” “What Post-Void MRIs May Reveal About Midline Radiotracer Activity on PSMA PET/CT” and “Do Bone Scans Over Stage Prostate Cancer? What a Multicenter Study Reveals.”)

Beyond the inherent limitations of a single-center study, the researchers noted the small cohort size, and conceded that subjectivity with PI-RADS scoring may limit broader extrapolation of the study findings to other facilities.


1. Shi J, Li D, Chen M, et al. The value of 68Ga-PSMA PET/MRI for classifying patients with PI-RADS 3 lesions on multiparametric MRI: a prospective single-center study. J Nucl Med. 2024 Mar 14:jnumed.123.266742. doi: 10.2967/jnumed.123.266742. Online ahead of print.

2. Emmett L, Papa N, Buteau J, et al. The PRIMARY score: Using intraprostatic 68Ga-PSMA PET/CT patterns to optimize prostate cancer diagnosis. J Nucl Med. 2022;63(11):1644-1650.

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