Factors predicting the early biochemical response to [177Lu]Lu-PSMA therapy in patients with metastatic castration resistant prostate cancer

Targeted radionuclide therapy with [177Lu]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 [177Lu]Lu-PSMA therapy. In this retrospective study, mCRPC patients, referred for [177Lu]Lu-PSMA therapy, were included. We retrieved the data of patients, undergone [177Lu]Lu-PSMA, from March 2019 to March 2021. 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 [177Lu]Lu-PSMA therapy for the biochemical response. Forty-three patients with a mean age of 69.8±10.2 were included. Bone and visceral metastases were present in 81.4% and 14.0% of the patients, respectively. Except for two, all patients had received hormone- and chemotherapy. The mean PSA level was 189.9±259.0 at baseline. Following one cycle of [177Lu]Lu-PSMA, “≥ 10% PSA response” and “≥ 50% PSA response” were seen in 81.4% and 44.2% of the patients, respectively. Patients with higher baseline PSA more frequently had ≥ 10% PSA response (p= 0.004). Also, the reduction in the PSA level correlated with baseline PSA (p=0.013, r=0.375). [177Lu]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 50%. Higher baseline PSA is correlated with the level of PSA response.