Head-to-head comparison of 68Ga-PSMA-11 PET with 99mTc-MDP bone scan for detection of bone disease in patients with prostate cancer with biochemical progression during ADT: A single center prospective study.

person Andrei Gafita Ahmanson Translational Theranostics Division, University of California, Los Angeles, CA info_outline Andrei Gafita, Rejah M. Alano, Matthew Rettig, John Shen, Wesley Robert Armstrong, Tristan Grogan, Sandy Liu, Matthias R. Benz, Johannes Czernin, Jeremie Calais

Authors person Andrei Gafita Ahmanson Translational Theranostics Division, University of California, Los Angeles, CA info_outline Andrei Gafita, Rejah M. Alano, Matthew Rettig, John Shen, Wesley Robert Armstrong, Tristan Grogan, Sandy Liu, Matthias R. Benz, Johannes Czernin, Jeremie Calais Organizations Ahmanson Translational Theranostics Division, University of California, Los Angeles, CA, University of California Los Angeles, Los Angeles, CA, UCLA Department of Medical Oncology, Los Angeles, CA, UCLA Department of Nuclear Medicine, Los Angeles, CA, UCLA Department of Medicine Statistics Core, Los Angeles, CA, Division of Hematology-Oncology, University of California, Los Angeles, Los Angeles, CA, University of California-Los Angeles, Los Angeles, CA Abstract Disclosures Research Funding Institutional Funding UCLA Background: 68 Ga-PSMA-11 PET/CT (PSMA-PET) was approved by the U.S. Food and Drug Administration in patients with prostate cancer (PCa) at primary staging or biochemical recurrence. A head-to-head comparison between PSMA-PET and conventional imaging (99mTc-MDP bone scan [BS] and CT) in men with advanced prostate cancer was not performed. We aimed to compare the detection rate of bone disease for PSMA-PET vs BS in men with PCa and with biochemical progression during androgen deprivation therapy (ADT). Methods: This was a prospective single-center, open-label, single-arm, head-to-head comparison, prospective phase 2 study (NCT04928820). A sample size of 102 men was required to achieve an 80.3% power to detect a difference of 12% positivity rate of bone disease in favor of PSMA-PET vs BS (35% vs 23%). Men with i) biopsy-proved PCa, ii) who had rising PSA levels on 2 successive occasions ≥1 week apart, iii) were receiving treatment with hormonal therapy, iii) and had an absolute PSA value ≥1 ng/ml were eligible. Men who were enrolled received PSMA-PET and bone scan within 30 days. The primary endpoint was detection rate of bone disease for PSMA-PET vs BS. Secondary endpoint was the number of bone lesions detected by PSMA-PET vs BS. Number of lesions was categorized into: 0 vs 1 vs 2 vs 3 vs 4 vs 5 vs > 5. A p value < 0.05 was considered statistically significant. Results: 22 men were enrolled between July 8, 2021 and June 9, 2022. The median patients age was 71 years (range: 56-94). The median time between scans was 12 days (range: 1-29). The median PSA value was 9.5 ng/ml (range: 1.2 – 1717). 11/22 (11%) patients had hormone-sensitive PCa, while 11/22 (50%) had castration-resistant PCa prior to receiving the scans. The positivity rate for bone disease was equal for PSMA-PET and BS in all cases: 7/22 (32%) patients had negative scans on both imaging modalities and 15 (68%) had ≥1 bone lesion detected on both imaging modalities (p = 1.00). In 15/22 (68%) men, both imaging modalities showed equal number of bone lesions: 0 lesions in 7/22 (32%) men and > 5 lesions in 8/22 (36%) men. In 3/22 (14%) men BS showed higher number of lesions, while in 4/22 (18%) men PSMA-PET showed higher number of lesions. No statistical difference was noticed between PSMA-PET and BS in number of bone lesions detected (p > 0.05). The trial was terminated early since these preliminary results gave already a 95% confidence interval of 81-100% for equivalent positivity rate of bone disease between PSMA-PET and BS. Conclusions: In this prospective study of patients with prostate cancer with rising PSA levels under hormonal therapy, 68 Ga-PSMA-11 PET and 99 mTc-MDP bone scan had similar detection rate for bone disease. Further studies investigating similar comparison between PSMA-PET and BS in clinically-relevant selected patient population are warranted. Clinical trial information: NCT04928820.

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