CYP2C9, CYP2D6, and CYP3A4 mRNA expression has unambiguously been detected in mammary gland.11,12 Strong protein expression of CYP2S1 and CYP3A4 has been associated with shorter survival time of breast carcinoma patients.13 Despite the knowledge about CYP2W1 substrate specificity is limited,14 its overexpression in colorectal carcinomas15 raises interest about future plans for CYP2W1-based cancer therapy.6 The gene discussed is CYP2D6; the disease is cancer.