Revisiting Skull Metastases of Prostate Cancer at Prostate-Specific Membrane Antigen (PSMA) Positron Emission Tomography/Computed Tomography Era: PSMA Uptake Characteristics and Oncological Outcomes

Objective: We aimed to evaluate prostate-specific membrane antigen (PSMA) uptake characteristics and the oncological outcomes in patients with skull metastases. Methods: The records of 345 serial PSMA positron emission tomography (PET)/computed tomography (CT) scans of 96 patients with metastatic prostate cancer (PCa) were evaluated retrospectively. Skull bone metastasis was detected in 18 patients (18/96, 18.7%), with a mean age of 72.4 ± 9.1 years, and in 40 PSMA PET/CT scans (40/345, 11.6%). Involved skull bones, PSMA uptake characteristics, and CT counterparts of metastatic lesions were centrally reviewed. Prostate specific antigen (PSA) levels at the time of skull metastasis detection and PSMA-detected other metastatic lesions were recorded. Results: All patients with a skull metastasis showed multiple other metastatic bone lesions, and 6 (33.3%) had visceral metastasis. Seven (38.9%) patients had solitary skull lesions, whereas 11 (61.1%) had multiple skull metastases. Twenty-two out of 37 (59.5%) metastatic lesions had no CT counterpart. The median SUVmax was significantly higher in metastatic lesions with a CT counterpart (median 9.09 vs. 4.63, P = .018). At a median follow-up of 23.4 mo (interquartile range [IQR] 8.7-34.1) after detection of skull metastasis, 5 out of 11 (45.5%) hormone-sensitive and all castration-resistant patients died of PCa. The median survival of patients with castration-resistant disease was 9.92 months. Conclusion: The majority of PSMA-detected skull metastases did not show a CT counterpart, which may explain why skull metastases were rarely detected before the PSMA PET-era. In high-volume metastatic prostatic cancer cases, 68Ga-PSMA PET/CT imaging field including the vertex, may enhance the accuracy in detecting tumor extent and metabolic tumor volume.