Hematologic toxicity in 177lu-PSMA-617 treatment for mCRPC: Unraveling the impact of PSMA PET bone tumor volume (PSMA-bTTV).

5075 Background: Lutetium-177 prostate-specific membrane antigen ( 177 Lu-PSMA-617) is a life-prolonging treatment approved by the FDA in metastatic castration-resistant prostate cancer (mCRPC), at a very late stage when there frequently reduced bone marrow reserve. We aim to report the incidence of hematologic toxicity during treatment and potential risk factors in a single-center study. Methods: This retrospective single-institution case series included mCRPC patients who underwent at least one cycle of 177 Lu-PSMA-617 treatment between June 2022 and January 2024. Hematological parameters were documented at baseline, 3 weeks after each treatment, and before each subsequent treatment administration. Then, we captured the nadir values for each parameter during treatment. Hematologic toxicities were assessed using the Common Terminology Criteria for Adverse Events v5.0, with Grades 3 and 4 considered significant. Multivariable logistic regression analyses were conducted to investigate the association between hematological adverse events and baseline characteristics including PSMA-bTTV, measured by semi-automatic contouring of the PSMA-expressing whole-body bone metastases on pre-treatment PSMA PET. Results: Our study included 138 mCRPC patients (median age: 73y, prior chemotherapy: 92%, prior radiation: 43.5%, bone involvement: 89.1%), who underwent a median of 3 cycles (IQR: 2-5) of 177 Lu-PSMA-617 treatment. At baseline, 8 (5.8%) patients had grade 3 anemia, 2 (1.4%) patients had grade 3 leukopenia, and 1 (0.7%) patient had grade 3 thrombocytopenia. Nadir values during treatment indicated that 23 (16.7%) had grade 3 anemia, 5 (3.6%) had grade 3 leukopenia, and 11 (8%) had grade 3 and 4 thrombocytopenia. Multivariable analysis of predisposing factors for hematologic adverse events showed that the PSMA-bTTV was significantly associated with occurrence of any grade ≥3 hematologic toxicity, anemia, and thrombocytopenia after adjusting for other baseline clinical variables (Table). Conclusions: Over 1 in 5 patients with mCRPC experienced significant hematologic adverse events during treatment with 177 Lu-PSMA-617. Bone tumor volume is a possible risk factor for developing significant hematologic toxicity. Table: see text