Objective: The objective of this research was to examine the prostate-specific membrane antigen (PSMA)-positive secondary tumor incidence in 68Ga-PSMA positron emission tomography/computed tomography (PET/CT) imaging in patients with prostate cancer (PCa).

Methods: Data from 605 68Ga-PSMA PET/CT images of 506 PCa patients used for staging or restaging were analyzed retrospectively. Further, documented separately, PSMA-positive lesions were found not to be PCa-related and were then suspected as secondary tumors. The results were analyzed from those lesions that were histopathologically verified.

Results: Nine patients (1.8%) had a PSMA-positive lesion that was believed to be a secondary tumor. Of these lesions, five (1%) were histopathologically confirmed, and secondary tumors were diagnosed (namely, squamous cell non-small cell lung cancer, papillary thyroid cancer (TCa) lymph node metastasis, minimally invasive TCa, colon cancer and liver metastases, and fibrohistiocytic tumor). The mean serum PSA value for patients diagnosed with secondary tumor was 29.42 (0.01-142.22) ng/mL. For PSMA-positive secondary tumor lesions, the mean maximum standard unit value was 9.74 (3.9-15).

Conclusion: Especially in the presence of atypical location and insufficient serum PSA values, PSMA-positive lesions should be considered secondary tumors, and differential diagnostic studies should be conducted.