Ahmed Al-Timimi - Research Center for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran
Reyhaneh Manafi-Farid - Research Center for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran
Babak Fallahi - Research Center for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran
Davood Beiki - Research Center for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran
Emran Askari - Nuclear Medicine Research Center, Mashhad University of Medical Sciences, Mashhad, Iran
Alireza Rezaei - Khatam PET/CT Center, Khatam Al-Anbia Hospital, Tehran, Iran
Zohreh Adinehpour - Khatam PET/CT Center, Khatam Al-Anbia Hospital, Tehran, Iran
Mohammad Eftekhari - Research Center for Nuclear Medicine, Tehran University of Medical Sciences, Tehran, Iran

Introduction: Targeted radionuclide therapy with [۱۷۷Lu]Lu-prostate-specific membrane antigen (PSMA) has shown promising results for the treatment of castration-resistant prostate cancer (mCRPC). Nevertheless, a proportion of patients do not respond to this therapy. Here, we aimed to evaluate the prognostic significance of the pretreatment pathologic and laboratory factors for the prediction of biochemical response to the first cycle of [۱۷۷Lu]Lu-PSMA therapy.Methods: In this retrospective study, mCRPC patients, referred for [۱۷۷Lu]Lu-PSMA therapy, were included. We retrieved the data of patients, undergone [۱۷۷Lu]Lu-PSMA, from March ۲۰۱۹ to March ۲۰۲۱. Multiple baseline pathologic and laboratory parameters were extracted and correlated with the response to the first cycle. The prostate-specific antigen (PSA) level was evaluated six weeks after [۱۷۷Lu]Lu-PSMA therapy for the biochemical response.Results: Forty-three patients with a mean age of ۶۹.۸±۱۰.۲ were included. Bone and visceral metastases were present in ۸۱.۴% and ۱۴.۰% of the patients, respectively. Except for two, all patients had received hormone- and chemotherapy. The mean PSA level was ۱۸۹.۹±۲۵۹.۰ at baseline. Following one cycle of [۱۷۷Lu]Lu-PSMA, “≥ ۱۰% PSA response” and “≥ ۵۰% PSA response” were seen in ۸۱.۴% and ۴۴.۲% of the patients, respectively. Patients with higher baseline PSA more frequently had ≥ ۱۰% PSA response (p= ۰.۰۰۴). Also, the reduction in the PSA level correlated with baseline PSA (p=۰.۰۱۳, r=۰.۳۷۵).Conclusion: [۱۷۷Lu]Lu-PSMA therapy results in the biochemical response in a considerable number of patients after one cycle. In nearly half of patients, PSA declines more than ۵۰%. Higher baseline PSA is correlated with the level of PSA response.

castration-resistant prostate cancer, mCRPC, Lu-PSMA, Radioligand therapy, PSA response