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Abstract Multiple myeloma is a genetically complex and heterogenous malignancy with a 5-year survival rate of approximately 60%. Despite advances in therapy, patients experience cycles of remission and relapse, with each successive line of therapy associated with poorer outcomes; therefore, therapies with different mechanisms of action against new myeloma antigens are needed. G protein–coupled receptor class C group 5 member D (GPRC5D) has emerged as a novel therapeutic target for the treatment of multiple myeloma. We review the biology and target validation of GPRC5D, and clinical data from early phase trials of GPRC5D-targeting bispecific antibodies, talquetamab and forimtamig, and chimeric antigen receptor T cell (CAR-T) therapies, MCARH109, OriCAR-017, and BMS-986393. In addition to adverse events (AEs) associated with T-cell–redirection therapies irrespective of target, a consistent pattern of dermatologic and oral AEs has been reported across several trials of GPRC5D-targeting bispecific antibodies, as well as rare cerebellar events with CAR-T therapy. Additional studies are needed to understand the underlying mechanisms involved in the development of skin- and oral-related toxicities. We review the strategies that have been used to manage these GPRC5D-related toxicities. Preliminary efficacy data showed overall response rates for GPRC5D-targeting T-cell–redirecting therapies were ≥64%; most responders achieved a very good partial response or better. Pharmacokinetics/pharmacodynamics showed that these therapies led to cytokine release and T-cell activation. In conclusion, results from early phase trials of GPRC5D-targeting T-cell–redirecting agents have shown promising efficacy and manageable safety profiles, including lower infection rates compared with B-cell maturation antigen- and Fc receptor-like protein 5-targeting bispecific antibodies. Further clinical trials, including those investigating GPRC5D-targeting T-cell–redirecting agents in combination with other anti-myeloma therapies and with different treatment modalities, may help to elucidate the future optimal treatment regimen and sequence for patients with multiple myeloma and improve survival outcomes. Video Summary

Abstract Chimeric antigen receptor (CAR) T-cell therapies are highly effective for multiple myeloma (MM) but their impressive efficacy is associated with treatment-related neurotoxicities in some patients. In CARTITUDE-1, 5% of patients with MM reported movement and neurocognitive treatment-emergent adverse events (MNTs) with ciltacabtagene autoleucel (cilta-cel), a B-cell maturation antigen-targeted CAR T-cell therapy. We assessed the associated factors for MNTs in CARTITUDE-1. Based on common features, patients who experienced MNTs were characterized by the presence of a combination of at least two variables: high tumor burden, grade ≥2 cytokine release syndrome (CRS) or any grade immune effector cell-associated neurotoxicity syndrome (ICANS) after cilta-cel infusion, and high CAR T-cell expansion/persistence. Strategies were implemented across the cilta-cel development program to monitor and manage patients with MNTs, including enhanced bridging therapy to reduce baseline tumor burden, early aggressive treatment of CRS and ICANS, handwriting assessments for early symptom detection, and extended monitoring/reporting time for neurotoxicity beyond 100 days post-infusion. After successful implementation of these strategies, the incidence of MNTs was reduced from 5% to

Abstract Identification of risk factors for early mortality (EM) in multiple myeloma (MM) patients may contribute to different therapeutic approaches in patients at risk for EM. This population-based study aimed to assess trends in EM and risk factors for EM among MM patients diagnosed in the Netherlands. All MM patients, newly diagnosed between 1989 and 2018, were identified in the Netherlands Cancer Registry. Patients were categorized into three calendar periods (1989–1998, 1999–2008, 2009–2018) and into five age groups (≤65, 66–70, 71–75, 76–80, >80 years). EM was defined as death by any cause ≤180 days post-diagnosis. We included 28,328 MM patients (median age 70 years; 55% males). EM decreased from 22% for patients diagnosed in 1989–1998 to 13% for patients diagnosed in 2009–2018 (P 70 years. Therefore, novel strategies should be explored to improve the outcome of patients at risk for EM.