['Functional role of Annexin A1 in tumorigenesis is poorly understood. The aim of this study was to investigate the relationship between Annexin A1 protein expression and pathological differentiation grade in biopsy samples from a large cohort of patients with oral squamous cell carcinoma (OSCC); and to evaluate the potential role of Annexin A1 on cell proliferation and tumorigenesis of OSCC.', 'We investigated the relationship between Annexin A1 expression by immunohistochemical staining and pathological differentiation grade of biopsy samples from 232 OSCC patients, and the relationship between Annexin A1 expression and cell proliferation as well as tumor formation using both in vitro and in vivo OSCC models.', 'Annexin A1 expression correlated significantly with pathological differentiation grade in OSCC patients, a lower Annexin A1 expression correlating with a poorer differentiation grade. Forced Annexin A1 overexpression in OSCC cell lines, CAL27 and Tca8113, significantly reduced the cell proliferation whereas down-regulation of Annexin A1 expression in OSCC cell line, HB96, significantly increased proliferation of HB96 cells. Tumors formed from CAL27 cells overexpressing Annexin A1 grown significantly slower compared to the parental CAL27 cells in nude mice and showed a significantly reduced nuclear Ki-67 labeling index. Interestingly, these tumors also showed a well differentiated histology pattern whereas the tumors formed from the parental cells were consistently moderately differentiated.'] Does annexin A1 down-regulation in oral squamous cell carcinoma correlate to pathological differentiation grade?