The MLH1 antibody is a crucial tool in molecular pathology, primarily used to detect the MLH1 protein, a key component of the DNA mismatch repair (MMR) system. MLH1. encoded by the *MLH1* gene on chromosome 3p22.2. forms heterodimers with other MMR proteins (e.g., PMS2) to correct DNA replication errors. Loss of MLH1 function, often due to mutations or epigenetic silencing, disrupts MMR, leading to microsatellite instability (MSI) and increased cancer risk. Germline *MLH1* mutations are linked to Lynch syndrome, a hereditary condition predisposing to colorectal, endometrial, and other cancers. In sporadic cancers, MLH1 deficiency is commonly caused by promoter hypermethylation.
Clinically, MLH1 immunohistochemistry (IHC) helps identify tumors with MMR deficiency. Absence of nuclear MLH1 staining guides further testing (e.g., *BRAF* mutation or methylation analysis) to differentiate Lynch-associated cancers from sporadic cases. It also aids in stratifying patients for immunotherapy, as MSI-high tumors often respond better to immune checkpoint inhibitors. Researchers additionally use MLH1 antibodies in Western blotting or immunofluorescence to study DNA repair mechanisms. Interpretation requires caution, as MLH1 loss may coexist with PMS2 loss due to their functional partnership. Overall, MLH1 antibody-based assays are vital in diagnostics, prognostics, and personalized oncology.