SP21 | SAFE AND EFFECTIVE USE OF MOSUNETUZUMAB IN A VERY ELDERLY PATIENT WITH RELAPSED/REFRACTORY FOLLICULAR LYMPHOMA: A CASE REPORT

Background: Mosunetuzumab, a CD20xCD3 bispecific antibody, has shown efficacy and a favorable safety profile in relapsed/refractory follicular lymphoma (FL). Clinical trials report durable responses with manageable toxicity, mostly low-grade cytokine release syndrome (CRS). However, real-world data in patients >85 years with comorbidities are lacking. Documenting feasibility in such cases is critical to expanding access to novel immunotherapies. Case Report: A female patient aged >89 was diagnosed in 2018 with grade II, stage IV FL and achieved complete remission with R-CHOP, in other center. In 2024, clinical relapse presented with left leg lymphedema and palpable left inguinal lymphadenopathy. PET-CT showed subdiaphragmatic nodal involvement with high metabolic activity (SUV max 7.99) and moderate uptake in supradiaphragmatic regions, including a small mediastinal node. Biopsy of the left inguinal lymph node confirmed recurrence of grade II follicular lymphoma. Rituximab monotherapy (4 doses) proved ineffective, confirming refractory disease. Despite advanced age and comorbidities, including chronic kidney disease (ClCr 32 mL/min), ECOG 1 and functional independence were preserved. Mosunetuzumab therapy was started after multidisciplinary evaluation. Five cycles were completed without dose delays, or modifications. Treatment was well tolerated. A single grade 2 CRS episode occurred after the first dose, with fever and desaturation, resolved promptly with tocilizumab (8 mg/kg). No immune effector cell-associated neurotoxicity syndrome (ICANS), severe cytopenias, or infections were observed. Interim PET after cycle 5 showed a Deauville Score of 2. The patient maintained autonomy and quality of life throughout treatment. Conclusion: This case supports the feasibility and safety of mosunetuzumab in very elderly patients. Key parameters for patient selection must include preserved ECOG status, controlled comorbidities, and close monitoring. Age and moderate renal dysfunction should not exclude patients from bispecific antibody therapy in appropriate settings. This experience adds real-world evidence to the growing body of data outside of strictly controlled clinical trial settings.