ERCC2 and colorectal carcinoma: The risks of CRC in XPD gene A allele carriers (GA/AA) (adjusted OR = 1.570, 95%CI = 1.201–1.976, P=0.001), hOGG1 gene G allele carriers (CG/GG) (adjusted OR = 3.031, 95%CI = 2.184–4.225, P<0.001) and XRCC4 gene T allele carriers (GT/TT) (adjusted OR = 2.793, 95%CI = 2.235–3.222, P<0.001) were significantly higher in patients who smoked ≥16 packs/year.