Other than cancer susceptibility, CYP3A4 also plays a key role in chemotherapy resistance, and a drug metabolism study on 108 cancer patients demonstrated that CYP3A4*22 carriers (rs35599367 C > T) exhibited reduced erythromycin N-demethylation activity by 40%, highlighting the importance of considering CYP3A4 polymorphisms in cancer treatment to maximize efficacy and to avoid unpredictable adverse events (Elens et al., 2013). Here, CYP3A4 is linked to cancer.