The Effect of ADT on PSMA Expression in Metastatic Prostate Cancer (ADTPSMA2)

The Effect of Androgen Deprivation Therapy on the Expression of Prostate Specific Membrane Antigen (PSMA) Evaluated With 18F-PSMA PET/CT in Treatment naïve Metastatic Prostate Cancer Patients

Thirty-five men with newly diagnosed, metastatic prostate cancer are scanned with 18F-PSMA 1007 PET/CT at baseline, 3 weeks after the initiation of GnRH-antagonist, at one year and at the time of castration resistant prostate cancer (CRPC). The aim of the study is to classify metastatic lesions into those with PSMA-flare and those without and determine their potential to progress during the follow-up until CRPC.

In metastatic prostate cancer androgen deprivation therapy (ADT) has been traditionally used as a first line approach. Based on histological studies, animal models and PSMA-PET imaging, it is known that administration of ADT increases prostate specific membrane antigen (PSMA) expression. Preliminary results of our previous prospective clinical trial (clinicaltrials.gov identifier: NCT03313726) with nine men demonstrated a heterogenous flare in PSMA expression 2-3 weeks after ADT, more evidently in bone metastases. Our hypothesis is that metastatic lesions having PSMA-flare respond differently to ADT and have different outcome than those without PSMA-flare. Therefore, the objective of the study is to demonstrate the PSMA-flare seen in bone lesions 3 weeks after ADT and then determine the potential predictive value of the phenomenon in the progression to castration resistant prostate cancer (CRPC). Thirty-five men with newly diagnosed, metastatic PC will undergo 18F-PSMA 1007 PET/CT before and 3 weeks after the initiation of sub-cutaneous injection of GnRH-antagonist (Degarelix, Firmagon®). A subgroup of 20 patients will receive an additional FDG PET/CT scan before ADT to investigate whether lesions with PSMA flare show a different metabolic behaviour on FDG PET. During the follow-up, 18F-PSMA 1007 PET/CT will be also performed once a year. Finally all patients will repeat 18F-PSMA 1007 PET/CT at the time of CRPC. In addition to imaging, PSA is measured, and blood drawn for androgen levels and biomarkers in three months interval.

Administration of GnRH antagonist (subcutaneous injection, 240 mg) after baseline 18F-PSMA 1007 PET/CT.Then 18F-PSMA 1007 PET/CT is repeated 3 weeks after ADT and at development of CRPC

18F-PSMA 1007 PET/CT before, 3 weeks after ADT, at 1 year and at CRPC in 35 patients. 18F-FDG PET/CT in a subgroup of 20 patients before ADT.

Comparison of mean increase of SUVmax in 18F-PSMA 1007 PET between bone lesions and prostatic lesions after the initiation of ADT

Inclusion Criteria: Age: 40 to 85 years old Language spoken: Finnish Diagnosis: Histologically confirmed adenocarcinoma of prostate Adequate histological sampling consisting of at least 3 biopsy samples from each lobe No previous surgical, radiation or endocrine treatment for prostate carcinoma Clinical stage:T1c-T4NanyM1 Serum creatinine ≤ 1,5 x ULN Mental status: Patients must be able to understand the meaning of the study Informed consent: The patient must sign the appropriate Ethical Committee approved informed consent documents in the presence of the designated staff Exclusion Criteria: Previous PC treatment Uncontrolled serious infection Prior usage of 5-ARI medication in past 12 months

Malaspina S, Ettala O, Tolvanen T, Rajander J, Eskola O, Bostrom PJ, Kemppainen J. Flare on [18F]PSMA-1007 PET/CT after short-term androgen deprivation therapy and its correlation to FDG uptake: possible marker of tumor aggressiveness in treatment-naive metastatic prostate cancer patients. Eur J Nucl Med Mol Imaging. 2023 Jan;50(2):613-621. doi: 10.1007/s00259-022-05970-y. Epub 2022 Sep 26.