Hematotoxicity after Radioligand Therapy with 177Lu-PSMA-617 in Patients with Metastastic Prostate Cancer

594 Introduction: Myelosuppression may be a dose-limiting factor in repeated cycles of radioligand therapy (RLT). This study aims to investigate the incidence, severity and reversibility of hematotoxicity in a large patient cohort with progressive metastatic prostate cancer undergoing RLT with 177Lu-PSMA-617. The impact of pre-existing risk factors and the cumulative administered activity were of particular interest. Methods: RLT was performed in 155 patients. Previous treatments included second-generation antiandrogenes (enzaltamide, abiraterone) in 115, at least one line of chemotherapy in 78, and 223Ra-dichloride in 66 patients. A mean activity of 6.7± 1.3 GBq 177Lu-PSMA-617 per cycle was administered in a median of 4 treatment cycles (IQR 2 to 5) at intervals of 6 to 8 weeks. Median cumulative activity was 19.0 GBq (IQR 11.4 to 35.2). Hematological parameters were measured at baseline, prior to each treatment course, 2 to 4 weeks thereafter and throughout follow-up. Toxicity was classified using Common Terminology Criteria for Adverse Events v5.0. Results: Significant treatment-induced hematotoxicity (grade 3 or 4) occurred in 18 patients (12 %), with anemia in 9% leukopenia in 5 % and thrombocytopenia in 5%. Bone marrow impairment was reversible throughout a median follow-up of 8 months (IQR 9 months) in all but two patients who died from disease progression within less than 3 months after RLT. Severe myelosuppression was significantly more frequent in patients with pre-existing grade 2 cytopenias (p=0.04) or high bone tumor burden (disseminated or diffuse based on PROMISE miTNM, p