Except for the coding region, a study in Japan found that CYP2B6 (g.−2320T > C, g.18492T > C, and g.−750T > C) in the non-coding region was also significantly associated with ADR (including leukopenia) of CYC (Nakajima et al., 2007). Here, CYP2B6 is linked to Decreased total leukocyte count.