CYP2C9 and cancer: Among them, the CYP2C9*2 (R144C) and CYP2C9*3 (I359L) variants occur at a high frequency among Caucasians with frequencies of 0.08–0.14 and 0.04–0.16, respectively,345–347 both yielding enzymes with decreased activity.347 Other variant CYP2C9 alleles with relatively low frequencies have also been reported, although no association studies between them and human cancer risk have been performed.