The accuracy of PSMA PET/CT for assessing intraprostatic lesions in patients with prostate cancer: An evaluation of the PI-RADS, PRIMARY and PSMA-expression score

SUMMARY

Background: Magnetic Resonance Imaging (MRI) is advised for the diagnosis of prostate cancer (PC), and PSMA PET/CT is used for distant staging of PC. Local staging of the primary tumour with PSMA PET/CT is currently not recommended, although the primary lesion can be visualised as well. Recently, two new tumour-assessing scores were developed to optimise the diagnostic accuracy of PSMA PET/CT for the primary tumour: the PSMA-expression score and the PRIMARY score.

Objective: To evaluate the performance of PSMA PET/CT and its PRIMARY and PSMA-expression scores in the assessment of intraprostatic lesions in patients with PC. Patients and methods: This is a retrospective analysis of patients treated with radical prostatectomy for PC in a single tertiary centre between 2019 and 2022. All patients underwent preoperative prostate MRI and 18F- or 68Ga-PSMA-11 PET/CT. The medical images were pseudonymized and retrospectively assessed by two radiologists and a nuclear medicine specialist. The PSMA PET/CTs were scored according to the PSMA-expression score (PROMISE V2 framework) and the PRIMARY score. The MRIs were scored using the PI-RADS system. The accuracy of the three different scores for diagnosing high-grade PC (ISUP grade ≥3) was evaluated.

Results: The PSMA-expression score demonstrated the highest accuracy for detecting high-grade PC, with an AUC of 0.76, outperforming the PI-RADS scores from reader 1 (AUC of 0.59) and reader 2 (AUC of 0.68) and the PRIMARY score (AUC of 0.69). It had a sensitivity of 72%, a specificity of 70%, a positive predictive value of 85%, and a negative predictive value of 51%.

Conclusion: PSMA PET/CT has a promising diagnostic accuracy to detect intraprostatic lesions of high grade in patients with PC. Further validation of the PSMA PET scoring systems is warranted.

Patient summary: In this study, the performance of PSMA PET/CT (the PRIMARY and PSMA-expression scores) to detect malignant lesions in the prostate was evaluated. PSMA PET/CT and these scoring systems seem promising to detect PC and could be of interest in cases where MRI is ambiguous.

(BELG J MED ONCOL 2025;19(2):46–53)