Pathologic outcome of incidentally detected tracer-avid lesions in 68Ga-PSMA-11 PET/CT for prostate cancer.

Abstract

Background: Prostate-specific membrane antigen (PSMA) PET is effective in identifying prostate cancer metastases. However, PSMA PET uptake has also been described in other lesions, including nonprostate malignancies and benign processes.

Purpose: To identify causes of unexpected radiopharmaceutical accumulation on PSMA PET.

Materials and methods: A total of 2,054 study reports representing 1,873 unique patients who had undergone ⁶⁸Ga-PSMA-11 PET/CT scans at a single large academic center from December 2015 to April 2022 were retrospectively reviewed for the mention of unexpected PSMA uptake not initially thought to represent metastatic prostate cancer. Scans with pathologic outcome were reviewed by 2 blinded readers for scan indication and lesion location and quantitative parameters.

Results: In 48 patients, the PSMA ligand-avid incidental lesions revealed 19 cases of second malignancies, 17 cases of prostate cancer, and 13 cases of benign lesions. The most common lesion locations were lung (14), thyroid (14), lymph nodes (8), and bowel (4). Benign lesions exhibited lower molecular imaging PSMA scores (median: 1; interquartile range [IQR]: 1.00-1.25; P = .017) than metastatic prostate lesions (median: 2; IQR: 1-3). Second malignancies were larger (median: 34 mm; IQR: 27-39 mm) than metastatic prostate cancer (median: 14 mm; IQR: 12-19 mm; P = .001) and benign lesions (median: 19 mm; IQR: 13.00-31.00 mm; P = .03). PSMA ligand-avid lesions in scans performed in the initial staging for prostate cancer were more commonly associated with a diagnosis of a secondary malignancy than with metastatic prostate cancer (0 vs 8 lesions, P = .008). Higher standardized uptake value maximum was observed for metastatic prostate cancer and second malignancy when compared with benign outcome.

Conclusion: Features that influence the probability of an incidental lesion representing a malignancy include lesion location, reason for the PSMA PET/CT study, and associated imaging features (size, standardized uptake value maximum, and molecular imaging PSMA score).