Purpose <p>Esophageal squamous cell carcinoma (ESCC) is a lethal gastrointestinal cancer. Metformin, a widely used drug for diabetes, exhibits anti-tumor properties, but the functional mechanism in ESCC metastasis remains unclear. This study aims to investigate the clinical relevance of p21-activated kinase 1 (PAK1) in ESCC metastasis and to determine whether metformin suppresses ESCC migration and invasion by targeting PAK1 to modulate focal adhesion (FA) dynamics.</p> Methods <p>PAK1 expression was examined in ESCC tissues and cells via immunohistochemistry, RT-qPCR, and Western blot, and its correlation with clinicopathological features was analyzed. The impact of metformin on ESCC proliferation, invasion, and migration was investigated by CCK-8, wound healing, and transwell assays. Lentiviral-mediated PAK1 overexpression and knockdown were performed to validate the functional role of PAK1 in metformin action. Focal adhesion dynamics and the Src-FAK-Paxillin signaling pathway were analyzed by immunofluorescence and Western blot.</p> Results <p>PAK1 was overexpressed in ESCC tissues and positively correlated with lymph node metastasis. Notably, ESCC patients with a history of metformin use exhibited lower PAK1 expression. Functional assays demonstrated that metformin significantly inhibited ESCC cell migration and invasion in a dose-dependent manner. Knockdown of PAK1 phenocopied the inhibitory effects of metformin, whereas PAK1 overexpression abrogated these effects. Mechanistically, PAK1 promoted immature focal adhesion formation by activating the Src-FAK-Paxillin pathway, which was effectively suppressed by metformin.</p> Conclusion <p>Metformin suppresses the Src-FAK-Paxillin signaling pathway and promotes FA maturation, primarily by downregulating PAK1, thereby inhibiting ESCC migration and invasion. This study provides a novel mechanism for repurposing metformin in ESCC treatment.</p>