Prostate penile metastasis: Incidence and imaging pattern on 68 Ga-PSMA PET/CT.

BACKGROUND: Prostate cancer commonly metastasises to bone and regional lymphatics and more rarely to locations such as the brain, skin and penis. Gallium-68 prostate-specific membrane antigen (68 Ga-PSMA) positron emission tomography/computed tomography (PET/CT) has widely become the routine imaging modality for prostate cancer staging and re-staging in Australia. The aim of this study was to retrospectively review all 68 Ga-PSMA PET/CT examinations performed to date at our institution to determine the frequency of penile metastases. METHODS: A total of 4860 68 Ga-PSMA PET/CT examinations were performed between 16/07/2014 and 31/10/2019. Radiology reports for each examination were filtered to identify those with the words 'penis' or 'penile'. Once identified, relevant reports and images were individually reviewed to confirm the presence of a PSMA-avid penile lesion. RESULTS: The incidence of penile metastasis of prostate cancer observed in this study was 0.1% with six examinations identified as having PSMA-avid penile lesions in five prostate cancer patients (age range: 71-88 years). The patients had a 1-8 year history of prostate cancer with varying severity of disease. Appearance of PSMA-avidity varied between single focal lesion, multiple focal lesions and diffuse lesion. CONCLUSIONS: An incidence of 0.1% in our study confirms the rarity of penile metastases of prostate cancer. Although rare, identification of prostate cancer penile metastases is important for appropriate treatment management and symptom-relief.