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Abstract: 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.

RESUMO

Background: Oral squamous cell carcinoma (OSCC) is the most frequently occurring malignant tumor of the head and neck region. Chk2 (Checkpoint kinase 2) is considered a tumor suppressor gene that acts on the cellular response to DNA damage. However, the role of Chk2 in OSCC prognosis is not yet fully understood. The objective of this study was to evaluate Chk2 immunoexpression in OSCC and to elucidate the association between its expression and clinicopathological parameters of prognostic importance, including overall survival, disease-free survival, and metastasis-free survival. Methods: Chk2 expression was analyzed in 101 samples from patients with OSCC using immunohistochemistry. We stratified the patients into high expression (> 66% of cells positive for Chk2) and low expression (< 66%) groups. Results: Chk2 showed high expression in 57.43% of OSCC. In our study, the expression of Chk2 did not correlate with any of the prognostic parameters evaluated. There was no difference between overall survival, metastasis-free survival, and disease-free survival according to Chk2 expression. Conclusion: Despite the great importance of Chk2 in the development of different types of cancer, our findings do not favor Chk2 as a prognostic marker in oral squamous cell carcinoma.

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RESUMO

O câncer de boca corresponde a cerca de 4% das doenças neoplásicas, e o carcinoma de células escamosas representa o tipo mais frequente, englobando cerca de 90 a 95% dos casos. O cigarro é o principal fator etiológico para o câncer de boca, causando danos ao DNA e mutações que se não reparadas levam ao surgimento de lesões. O dano ao DNA associado ao cigarro tem sido estudado em diferentes tipos de câncer, mas ainda pouco explorado em relação ao câncer de boca. Checkpoint kinase 2 (CHK2) e P53 são proteínas que estão envolvidas no processo de checagem do ciclo celular, sendo responsáveis pelo reparo ao dano ao DNA. A proteína H2AX é uma histona nuclear que sofre fosforilação em resposta aos danos ao DNA, principalmente às quebras da dupla cadeia. O objetivo deste estudo foi avaliar a resposta a danos no DNA através da expressão de CHK2, γH2AX e TP53 entre fumantes e não fumantes com carcinoma de células escamosas de boca (CCEB). Além disso, foram analisadas associações entre imuno-expressão das proteínas estudadas, dados clínico-patológicos e classificação histopatológica. Foram incluídos 35 indivíduos (18 não fumantes e 17 fumantes) com CCEB de língua e soalho bucal. Reação imuno-histoquímica foi realizada para γH2AX para identificação de quebras de fita dupla, CHK2 e TP53 para avaliação da indução de parada do ciclo celular. Análises descritivas e estatísticas foram realizadas. A pesquisa foi composta por 22 homens (62,8%) e 13 mulheres (37,2%), com idade média de 63,9 anos. Entre os não fumantes, 50% apresentaram tumores bem diferenciados, enquanto que fumantes mostraram maior número em moderadamente diferenciados e pouco diferenciados (35,3% cada). No geral, 31 (88,6%) casos foram positivos para CHK2, 27 (77,2%) foram positivos para γH2AX e 23 (65,7%) foram positivos para TP53. Não foi observada associação entre essas proteínas com hábitos de fumar e não fumar (p> 0,05). Semelhanças entre os padrões imuno-histoquímicos de CHK2, γH2AX e TP53 em fumantes e não fumantes com CCEB foram observadas neste estudo, assim como entre os parâmetros clínico-patológicos. De forma geral, os resultados indicaram expressão positiva para essas proteínas no CCEB. Este estudo fornece informaçãoes sobre o dano ao DNA na carcinogênese oral.

Oral cancer accounts for about 4% of neoplastic diseases, and squamous cell carcinoma is the most common type, accounting for about 90 to 95% of cases. Cigarette smoking is the main etiological factor for oral cancer, causing DNA damage and mutations that, if not repaired, lead to lesions. Cigarette-associated DNA damage has been studied in different cancers, but is still poorly explored in relation to oral cancer. Checkpoint kinase 2 (CHK2) and P53 are proteins that are involved in the cell cycle checking process and are responsible for repairing DNA damage. The H2AX protein is a nuclear histone that undergoes phosphorylation in response to DNA damage, especially double strand breaks. The aim of this study was to assess the DNA damage response through the expression of checkpoint kinase 2 (CHK2), γH2A histone family member X (γH2AX) and TP53 among smokers and non-smokers with oral squamous cell carcinoma (OSCC). In addition, associations amongst immunoexpression of studied proteins, clinicopathologic data and histopathological grading were analyzed. Thirty-five individuals (18 nonsmokers and 17 smokers) with OSCC of the tongue and/or floor of the mouth were included. Immunohistochemistry was carried out for γH2AX for identification of double-strand breaks, CHK2 and P53 for evaluation of the induction of cell cycle arrest. Descriptive and statistical analyses were performed. The survey consisted of 22 males (62.8%) and 13 females (37.2%), with a mean age of 63.9 years. Fifty percent of non-smokers OSCC were well-differentiated tumors, whereas for smokers, OSCC were moderately differentiated and poorly differentiate tumors, equally (35.3% each). Overall, 31 (88.6%) cases were CHK2-positive, 27 (77.2%) were γH2AX-positive and 23 (65.7%) were TP53-positive. No association among these proteins with smoking and non-smoking habits was observed (p>0.05). Similarities in the CHK2, γH2AX and P53 immunohistochemical staining pattern were observed between smokers and non-smokers with OSCC in this survey, and the immunoexpression was not associated with clinicopathologic parameters. Overall, the results indicated consistent expression of these proteins in OSCC. This study provides information about the DNA damage in oral carcinogenesis.

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