Cancer is defined as a multifactorial disease resulting from complex interactions between extrinsic and intrinsic factors. Among the main intrinsic factors are the genetic and/or epigenetic alterations in genes involved with the carcinogenesis process. The identification and characterization of these genes may provide a better understanding of the molecular basis of cancer. Considering the importance of alterations in XRCC1, MRHFR and EGFR genes in various pro-carcinogenic pathways, it is extremely important to investigate the effects of functional polymorphisms in these genes and their molecular consequences in cancer susceptibility.The objective of this study was to identify possible associations between single nucleotide polymorphisms (SNPs) Arg194Trp (XRCC1) e Ala222Val (MTHFR) e Arg521Lys (EGFR) with the development of gastric and breast cancers in the population of Belém-PA, in a case-control study. Furthermore, the control of genomic ancestry was held to avoid spurious results arising from population substructuring in the groups investigated. Molecular analysis of SNPs was carried out by TaqMan. Statistical analyses were performed using the program SPSS v.20 and to estimate the interethnic admixture we used the program STRUCTURE v.2.2. Regarding polymorphisms Arg194Trp, Ala222Val we did not observe any significant association with susceptibility to breast and gastric tumors (P > 0.05).For the polymorphism Arg521Lys, in a first moment (univariate analysis), a significant effect for susceptibility to cancers investigated was found (P = 0.037). However, after genomic control for African and European ancestries, this result has proved to be spurious (P = 0.064). Regarding ancestries, our results showed a strong association of African ancestry with susceptibility to gastric and breast cancers (P = 0.010, OR = 76,723; 95% CI = 2.805 - 2098.230) whereas for European contribution a protective effect was found (P = 0.024, OR = 0071, 95% CI = 0.007-0.703). In conclusion, our study presented the evidence that the African and European genomic ancestries are important factors related to susceptibility to gastric and breast cancers. Regarding Arg521Ly polymorphism, further studies are necessary to confirm whether the association is indeed spurious.
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