Involvement of repair genes in oral cancer: A systematic review.  Among the types of cancers that may occur in the oral cavity, squamous cell carcinomas (SCC) of the mouth have a higher incidence and are associated with increased rates of morbidity and mortality. Among steps from the beginning to the progression of the tumour, DNA Repair System is highlighted. The present study aims to conduct a systematic review of the literature on the expression of the repair genes hMSH2 and hMSH6 in patients with SCC in the mouth and oropharyngeal region. The search was performed in databases such as PubMed, Lilacs, and Scielo and included articles published in English from 1999 until 2015. The search in the above-mentioned databases initially yielded 15 scientific articles related to the proposed objective. After a detailed analysis of each of them, only 8 were included in the present review, precisely because they met the inclusion criteria determined in the method. All the reviewed works were unanimous in recognizing the veracity and complexity of the Genomic Repair System, also called Mismatch Repair System, confirming the participation of repair gene proteins (such as hMSH2 and hMSH6) in patients with oral cancer and even of lesions that are susceptible to malignization. SIGNIFICANCE OF THE STUDY: Worldwide, there are an estimated 300 thousand new cases of oral cancer per year. Studies have shown a greater risk in individuals who are smokers and alcohol consumers in developing mouth cancer. Many steps are observed from the beginning to the progression of the tumour, highlighted among them is the moment in which genetic, and epigenetic alterations will interfere in the functioning of the DNA Repair System. This work presents a survey of current knowledge about the involvement of repair genes, especially those of the MutSα system, in the development and progression of oral cancer.