Association of immunoglobulin replacement with infection and mortality outcomes in multiple myeloma patients receiving bispecific antibodies: A TriNetX analysis.

e19526 Background: Bispecific antibodies have transformed the treatment landscape for relapsed or refractory multiple myeloma (MM) but are associated with high rates of serious infections. Immunoglobulin replacement therapy is variably used in clinical practice, and its impact on infectious outcomes in this setting remains incompletely characterized. We evaluated the association of early immunoglobulin replacement and infection and mortality outcomes in MM patients treated with bispecific antibodies. Methods: Using TriNetX, a federated network of de-identified electronic health records from participating healthcare organizations, we identified adults aged ≥18 years with MM who initiated bispecific antibody therapy (teclistamab, elranatamab, or talquetamab). Patients receiving immunoglobulin replacement within one month of bispecific initiation were compared with those who did not receive immunoglobulin replacement. Cohorts were propensity score–matched 1:1 on demographic factors, comorbidities, and prior myeloma therapies. The primary outcome was serious infection within 90 days. Ninety-day all-cause mortality was assessed as a secondary outcome. Results: After matching, 858 patients were included (429 per cohort). Serious infections occurred in 13.3% of patients receiving immunoglobulin replacement compared with 19.3% of those who did not (p = 0.016). Ninety-day mortality was 9.1% in the immunoglobulin group and 19.8% in the no-immunoglobulin group (p < 0.001). Conclusions: In this real-world cohort of MM patients treated with bispecific antibodies, early immunoglobulin replacement was associated with lower risks of serious infection and early mortality. These findings suggest a potential role for immunoglobulin replacement in reducing early infectious risk among patients receiving bispecific antibodies and support further prospective evaluation.