CYP2A6 and non-small cell lung carcinoma: One clinical study demonstrated an association of the CYP2A6*4 allele with exposure to 5-FU in non-small-cell lung cancer patients receiving S-1, while another study suggested that exposure to CDHP, which affects the metabolism of 5-FU, is the key determinant of variability in 5-FU efficacy following S-1 administration (Fujita et al, 2008; Kaida et al, 2008).