A systematic review and meta-analysis estimated the frequency of second primary malignant neoplasms (SPMs) after T-cell-engaging bispecific antibody therapy in adults with non-Hodgkin lymphoma and multiple myeloma. The study pools data across 20 studies (26 cohorts; 2,551 patients) and reports measurable long-term safety signals despite generally limited follow-up in the underlying trials. Researchers searched PubMed and Embase through October 1, 2025, following a PROSPERO-registered protocol and PRISMA-guided methods. Across eight included studies reporting total SPMs, the random-effects estimate was 3.5% (95% CI 1.8–6.9) at a median follow-up of 17.4 months. The analysis also found pooled estimates of 2.2% (95% CI 1.5–3.1) for SPMs leading to treatment discontinuation and 1.4% (95% CI 1.1–1.9) for SPMs leading to death. Authors reported no prespecified covariates—such as follow-up duration, disease category, prior therapy courses or age—were associated with total SPM rates, underscoring the need for longer observational data as bispecifics move earlier in treatment.