MTSS1 is a ubiquitously expressed intracellular protein that functions primarily as a multifunctional regulator of actin cytoskeleton dynamics and membrane architecture 1. Through its I-BAR and WH2 domains, MTSS1 acts as a scaffolding protein that interacts with actin and associated proteins to regulate cytoskeletal organization 2. Beyond its core cytoskeletal functions, MTSS1 modulates cell-cell contacts, cell differentiation, lipid metabolism, and vesicle formation, and serves as a scaffold for E3 ubiquitin ligases 1. Clinically, MTSS1 functions as a tumor suppressor in multiple cancer types. Reduced or absent MTSS1 expression is characteristic of advanced and metastasizing cancers, with downregulation observed in bladder carcinoma, tongue squamous cell carcinoma, and oral squamous cell carcinoma 234. MicroRNA-mediated suppression of MTSS1 (via miR-96 and miR-182-5p) promotes cancer cell proliferation and metastasis in tongue and oral cancers 34. In acute myeloid leukemia, MTSS1 downregulation at relapse contributes to therapy resistance and increased leukemic stem cell function 5. Beyond cancer, MTSS1 plays a sex-specific protective role against dilated cardiomyopathy, with reduced expression showing cardioprotective effects in females 6. Notably, MTSS1 is never mutated despite pathologic consequences of dysregulation, and gene ablation, while affecting embryonic development, is not universally lethal 1.