⁶⁸Ga-PSMA PET/CT Replacing Bone Scan in the Initial Staging of Skeletal Metastasis in Prostate Cancer: A Fait Accompli?

We compared the findings of technetium-99m–10-metacyloyloxydecyl dihydrogen phosphate (99mTc-MDP) bone scintigraphy and 68Ga–prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) in 113 patients who underwent initial skeletal staging for prostate cancer. 68Ga-PSMA PET/CT was found to be better than 99mTc-MDP bone scintigraphy because of ability to additionally detect lytic and bone marrow lesions. 68Ga-PSMA PET/CT could potentially replace bone scan for initial staging of skeletal metastases. Purpose: 68Ga ligands targeting prostate-specific membrane antigen (PSMA) are rapidly emerging as a significant step forward in the management of prostate cancer. PSMA is a type II transmembrane protein with high expression in prostate carcinoma cells. We prospectively evaluated the use of 68Ga-PSMA positron emission tomography/computed tomography (PET/CT) in patients with prostate cancer and compared the results to those for technetium-99m (99mTc)-10-metacyloyloxydecyl dihydrogen phosphate (MDP) bone scintigraphy (BS). Patients and Methods: A total 113 patients with biopsy-proven prostate cancer referred for standard-of-care BS were prospectively enrolled onto this study. 68Ga-PSMA PET/CT was performed after BS. Metastasis diagnosed on each technique was compared against a final diagnosis based on CT, magnetic resonance imaging, skeletal survey, clinical follow-up, and histologic correlation. Results: Ninety-one bone lesions were interpreted as bone metastases in 25 men undergoing 68Ga-PSMA PET/CT compared to only 61 lesions in 19 men undergoing 99mTc-MDP BS. Of the 7 bone scans that missed skeletal metastases, 54% of these missed lesions were due to either marrow or lytic skeletal metastases. The median standardized uptake value in all malignant bone lesions was 13.84. 68Ga-PSMA PET/CT showed significantly higher sensitivity and accuracy than BS (96.2% vs. 73.1%, and 99.1% vs. 84.1%) for the detection of skeletal lesions. For extraskeletal lesions, 68Ga-PSMA PET/CT showed an additional 96 unexpected lesions with a median standardized uptake value of 17.6. Conclusion: 68Ga-PSMA PET/CT is superior to and can potentially replace bone scan in the evaluation for skeletal metastases in the clinical and trial setting because of its ability to detect lytic and bone marrow metastases.