A prematurely terminated phase 2 trial has revealed that PSMA PET/CT demonstrates comparable efficacy to standard bone scans combined with CT in detecting bone metastasis in prostate cancer patients. The study, which enrolled 22 patients, was halted following the FDA's approval of PSMA radiotracers in 2022, which led to widespread insurance coverage and reduced patient accrual. Despite the early termination, the findings offer valuable insights into the diagnostic capabilities of PSMA PET/CT.
The trial enrolled patients between July 2021 and June 2022 with a median age of 71 years and a median PSA of 8.5 ng/mL. The patient cohort had varying prior treatments, including radical prostatectomy (32%), prostate-directed radiotherapy (59%), and chemotherapy (36%). The primary objective was to compare the detection rates of bone metastasis between 68Ga-PSMA PET/CT and 99mTc-MDP bone scan plus CT.
Bone Metastasis Detection
Results indicated that both PSMA PET/CT and bone scan plus CT had identical per-patient detection rates for bone lesions (p=1.0). Specifically, both scans detected bone lesions in 16 patients (73%) and no bone lesions in six patients (27%). While PSMA PET/CT detected more bone lesions in six patients (27%), and bone scan plus CT detected more in two patients (9.1%), the difference was not statistically significant (p=0.09).
Extra-Osseous Metastasis Detection
Notably, PSMA PET/CT demonstrated a superior detection rate for extra-osseous lesions compared to CT alone (p=0.023). PSMA PET/CT identified extra-osseous metastasis in 13 patients (59%), while CT alone detected it in only six patients (27.3%). This suggests that PSMA PET/CT may offer a more comprehensive assessment of disease spread beyond bone involvement.
Inter-Reader Agreement
Inter-reader agreement was high for both imaging modalities in detecting bone lesions, with no significant difference between PET/CT and bone scan plus CT (96% versus 82%, p=0.25). Kappa coefficients for inter-reader comparisons ranged from 0.89-1 for PSMA PET/CT and 0.58–0.89 for bone scan plus CT, indicating substantial to almost perfect agreement.
Implications and Limitations
Although the trial was limited by its premature termination and small sample size, the findings support the use of PSMA PET/CT as a valuable imaging modality in prostate cancer. The comparable detection rates for bone metastasis, coupled with the superior detection of extra-osseous lesions, suggest that PSMA PET/CT could potentially replace or complement standard bone scans in certain clinical scenarios. The study's authors note that the FDA approval and subsequent widespread adoption of PSMA radiotracers significantly impacted the trial's ability to accrue patients, highlighting the rapidly evolving landscape of prostate cancer imaging.
