The specific expression of CYP2C9 in the axons and synapses of brain neurons may be related to some brain diseases, and the mutation allele frequency of CYP2C9 is higher in 23 tumor samples, such as breast tumor and brain tumor, which indicates that CYP2C9 may be related to tumor [29, 30]. This evidence concerns the gene CYP2C9 and breast neoplasm.