Based on the existing gaps regarding the DNA methylation profile in the context ofchemoinduced oral mucositis and the importance of genes involved in oxidative andinflammatory stress mechanisms in the pathobiology of this condition, our objectivewas to investigate the DNA methylation profile in the CAT, SOD3,IL6 and TNF-α genes in the oral mucosa ofoncopediatric patients treated with MTX® in an attempt to identifymarkers of oral mucositis or exposure to chemotherapy. The gene discussed is CAT; the disease is oral mucositis.