Presentation Authors: Otto Ettala*, Simona Malaspina, Terhi Tuokkola, Peter Boström, Jukka Kemppainen, Turku, Finland
Introduction: Cell lines and animal models have demonstrated that prostate specific membrane antigen (PSMA) expression is altered after initiation of androgen deprivation therapy (ADT). However, the phenomenon is poorly studied in humans. The aim of the study is to evaluate the effect of ADT on PSMA expression by repeated 68Ga-PSMA-11-PET/MRI scans.
Methods: In this prospective, registered (NCT03313726) trial, men with newly diagnosed prostate cancer with high risk of metastasis underwent 68Ga-PSMA-11-PET/MRI immediately before and three times (within 8 weeks) after the initiation of ADT (Degarelix, 240mg). SUVmax measurements on primary tumour, lymph node and bone metastasis were performed.
Results: The nine men included were all diagnosed with Gleason grade group 5 prostate cancer. Of those, three represented with locally advanced and six with metastatic disease. After ADT, all men reached castration level (s-testo < 1.7nmol/L) within 10 days. In total, 16 prostate, 16 lymph node and 23 bone lesions were detected. In patient and lesion levels, a heterogeneous effect of ADT was observed. SUVmax trends in different lesions are demonstrated in Figure 1. In 5 (31%) prostatic lesions an increasing trend in SUVmax was observed, whereas in lymph nodes and bony metastasis the increase was seen in 7(44%) and 10(57%) lesions, respectively. In these lesions with SUVmax increase, the peak value (a mean of 13% increase in SUVmax in prostatic lesions, 9% in lymph nodes and 47% in bony metastasis) was reached within 2-3 weeks. In one patient, three new bony lesions were detected at week two.
Conclusions: PSMA expression evaluated with 68Ga PSMA-11-PET is affected heterogeneously by ADT. Bony lesions seem to have the most prominent increase in SUVmax. No substantial decrease in SUVmax was observed, indicating that imaging with 68Ga PSMA-11-PET is feasible even after castration level is achieved.