CYP2A6 and cancer: Similar findings were demonstrated in vivo in Japanese cancer patients such that individuals with the CYP2A6*4 allele had a higher plasma area under the concentration-time curve from 0 to 10 h (AUC0–10) for tegafur and a lower AUC0–10 for 5-fluorouracil compared to patients without the gene deletion; this suggests that CYP2A6*4 individuals are experiencing less exposure to the active metabolite 5-fluorouracil, potentially resulting in reduced therapeutic efficacy [138].