A recent phase 2 trial has explored the efficacy of PSMA-PET/CT in comparison to traditional bone scans for staging metastatic prostate cancer in patients progressing on androgen deprivation therapy. The study, led by Jeremie Calais, MD, PhD, a nuclear medicine physician at the University of California, Los Angeles, aimed to determine if PSMA-PET could offer a superior detection rate compared to bone scans in this patient population. The results indicated that both imaging modalities demonstrated comparable detection rates on a per-patient basis.
The trial (NCT04928820) was initiated before PSMA-PET received FDA approval, with the intention of enrolling 100 patients. The premise was to offer patients access to PSMA-PET scans within a research setting, contingent upon also undergoing a bone scan for comparison. However, following FDA approval of PSMA-PET, recruitment became challenging as patients could readily access the scan through standard clinical pathways. Consequently, the trial was terminated prematurely after only 20 patients were enrolled.
Study Design and Findings
The original hypothesis posited a 35% detection rate for PSMA-PET/CT versus a 23% detection rate for bone scan/CT. The study focused on patients with early-stage mCRPC, not those with very advanced disease. Both PSMA-PET and bone scans were evaluated by three blinded readers, with a majority scoring system (2 vs 1) used to resolve disagreements. Despite the early termination, the data from the initial 20 patients suggested that achieving a statistically significant difference in detection rates would have been unlikely, as the two imaging methods performed similarly in this subset.
While lesion-level analysis indicated that PSMA-PET detected more lesions, the per-patient analysis revealed no significant difference between the two modalities. Specifically, there were no patients who were bone scan positive and PSMA-PET negative, or vice versa.
Implications and Context
Bone scans have been the standard imaging method for staging metastatic prostate cancer for decades, leveraging the bone tropism of prostate cancer metastases. PSMA-PET has emerged as a valuable tool in prostate cancer staging over the past 5 to 10 years. In primary staging, untreated disease, and biochemical recurrence settings, PSMA-PET has demonstrated superiority over bone scans due to its higher specificity and accuracy, with bone scans often yielding false positives when metastasis prevalence is low.
However, in more advanced patient populations, such as those with metastatic castration-resistant prostate cancer, the specificity of bone scans increases due to the higher prevalence of bone metastasis. This study sought to address the comparative effectiveness of these two modalities in this specific patient group.
Conclusion
Although the trial was underpowered due to early termination, the findings suggest that in patients with early mCRPC, bone scans remain a viable imaging option, performing comparably to PSMA-PET on a per-patient detection basis. Further research with larger sample sizes may be warranted to explore subtle differences between the two modalities.
