Multi-Omics Analysis and Experimental Validation Identify RAD51 as a Key Biomarker in OSCC.

Oral squamous cell carcinoma (OSCC) is an aggressive malignancy associated with high morbidity and mortality. RAD51 recombinase (RAD51), a central DNA repair protein, plays a crucial role in homologous recombination and has been implicated in cancer progression through mechanisms such as genomic instability, chemoresistance and immune modulation. However, its specific function and regulatory mechanisms in OSCC remain incompletely elucidated. We conducted an integrated multiomics analysis including differential expression, single-cell transcriptomics, prognostic evaluation, functional enrichment and immune infiltration profiling. Experimental validation was performed using siRNA-mediated RAD51 knockdown in OSCC cell line HSC-3, followed by functional assays to assess proliferation, migration, invasion, reactive oxygen species (ROS) accumulation and chemosensitivity. RAD51 was significantly overexpressed across multiple cancers, including OSCC, and exhibited high diagnostic accuracy for OSCC (AUC = 0.956). Single-cell RNA sequencing revealed elevated RAD51 expression in malignant and proliferating T cells, associating it with aggressive phenotypic traits. High RAD51 expression predicted poor prognosis in OSCC and other cancers. Functional analyses indicated its involvement in the Fanconi anaemia pathway, DNA damage repair and cell cycle regulation. Immune infiltration analysis revealed significant negative correlations with multiple immune cell subtypes and tumour microenvironment scores. Experimentally, RAD51 knockdown suppressed malignant behaviours and enhanced ROS production and chemosensitivity in HSC-3 cells. RAD51 drives OSCC progression by enhancing malignant phenotypes, suppressing immune infiltration, promoting aberrant DNA repair, elevating oxidative stress and promoting therapy resistance. These findings support RAD51's potential as both a prognostic biomarker and a therapeutic target in OSCC.