Tobacco smoking involves a high risk of human malignancies, including oral cancer, because it contains multiple carcinogens that cause genetic instability. Thus, a worse prognosis would be expected for cancer patients who are smokers. The aim of this study was to assess the DNA damage response through the expression of checkpoint kinase 2 (CHK2), H2A histone family member X (H2AX), and P53 among smokers and non-smokers with oral squamous cell carcinoma (OSCC). Associations between immunoexpression of proteins and clinicopathological data and histopathological grading were also analyzed. A total of 35 individuals (18 non-smokers and 17 smokers) with OSCC of the tongue and/or floor of the mouth were included. Immunohistochemistry for H2AX was conducted for the identification of double-strand breaks, CHK2, and P53 to evaluate the expression of this protein in cell cycle regulation. The sample consisted of 22 males and 13 females, with a mean age of 63.9±11.8 years. OSCC of non-smokers were well-differentiated tumors in 50% of the cases, and those of smokers were equally distributed into moderately differentiated and poorly differentiated tumors (35.3% each). Overall, 31 (88.6%) cases were CHK2-positive, 27 (77.1%) were H2AX-positive, and 23 (65.7%) were P53-positive, with no difference between smokers and non-smokers (p > 0.05). No association was found between proteins and clinicopathologic data (p > 0.05). Similarities in CHK2, H2AX, and P53 immunohistochemical staining patterns were observed between smokers and non-smokers, and immunoexpression was not associated with clinicopathological parameters. However, the findings indicated consistent expression of these proteins in OSCC.
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