A recent phase II trial has revealed that prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) demonstrates comparable bone metastasis detection rates to planar bone scan plus CT in prostate cancer patients experiencing biochemical progression while on androgen deprivation therapy (ADT). The findings suggest that bone scan plus CT can continue to serve as a cost-effective and readily accessible restaging modality in this patient population.
The prospective, single-arm, head-to-head trial (NCT04928820) aimed to enroll 102 men with prostate cancer who had biochemical progression (rising prostate-specific antigen [PSA] ≥ 1 ng/mL) during ADT. Due to slow accrual following the approval of PSMA PET radiotracers in the U.S. and a lack of a statistical signal between the two imaging modalities on interim analysis, the trial was closed early after enrolling 22 men between July 2021 and June 2022.
All patients underwent 68Ga-PSMA-11 PET/CT and 99mTc-MDP planar bone scans, which were independently interpreted by three central readers. The primary endpoint was the per-patient bone metastasis detection rate of PSMA PET/CT versus planar bone scan and CT. Secondary endpoints included comparing the number of bone metastases detected per patient and the inter-reader agreement of each imaging modality.
The median PSA was 8.5 ng/mL (interquartile range: 1.6-77.6). There was 100% agreement between the two scans in terms of positive or negative findings. Six patients (27%) had negative findings, and 16 patients (73%) had positive findings on both scans. PSMA PET/CT and bone scan plus CT detected an equal number of bone lesions for 14 patients (64%). PSMA PET/CT detected more bone lesions for six patients (27%), while bone scan plus CT detected more bone lesions for two patients (9.1%) (p = 0.092).
The inter-reader agreement rates for PSMA PET/CT and bone scan plus CT were 96% and 82%, respectively (p = 0.25). According to the researchers, these results suggest that in men with biochemical progression during ADT, 68Ga-PSMA-11 PET/CT and 99mTc-MDP planar bone scan plus CT had identical bone metastasis detection rates.
Implications for Clinical Practice
The study's findings support the continued use of bone scan plus CT as a viable option for restaging in patients with biochemical progression of prostate cancer. Given its cost-effectiveness and accessibility, bone scan plus CT remains a valuable tool in resource-limited settings or when PSMA PET/CT is not readily available.
Study Limitations
The authors noted that the early closure of the trial due to slow accrual and the relatively small sample size may limit the generalizability of the findings. Further studies with larger cohorts are warranted to validate these results and explore potential differences in lesion detection between the two imaging modalities.
