A2ML1 (alpha-2-macroglobulin like 1) is a monomeric protease inhibitor that functions through a unique 'trapping' mechanism conserved across the A2M superfamily 1. The protein contains a bait region with cleavage sites for diverse proteinases; upon cleavage, conformational changes trap the protease while a thioester bond mediates covalent binding 1. This mechanism allows A2ML1 to inhibit multiple protease classes including serine and metalloproteinases, reducing substrate access to trapped enzymes 1. A2ML1 is expressed at the maternal-fetal interface during pregnancy, suggesting roles in immunotolerance and placental development 2. Clinically, A2ML1 variants are associated with otitis media susceptibility; sixteen novel damaging variants were identified in affected populations, with lower A2ML1 expression correlating with disease 3. Beyond ear disease, A2ML1 represents an emerging oncogenic biomarker: elevated expression promotes pancreatic cancer progression via KRAS/MAPK pathway activation and epithelial-mesenchymal transition 4, while paradoxically serving as a negative prognostic marker in non-small cell lung cancer and cervical cancer 56. Conversely, lower A2ML1 expression correlates with worse esophageal squamous cell carcinoma prognosis, suggesting context-dependent tumor roles 7. A2ML1 variants are also implicated in RASopathies 8, broadening its developmental significance.