Although it has been stated that the presence of a methylated MGMT allele can only be attributed to neoplastic cells [8,10,92], some authors have demonstrated that MGMT promoter methylation may occur in non-neoplastic central nervous system tissue [3] or in normal-appearing mucosa several centimetres away from digestive tumours [56,93]. The gene discussed is MGMT; the disease is digestive system neoplasm.