This theory is supported by some studies [33,35,36] whose results demonstrated that some CYP isoforms (such as CYP1B1, CYP1A1, CYP2C19, CYP2D6, CYP2E1, CYP3A4 or CYP3A5) are altered in RCC patients. The gene discussed is CYP2E1; the disease is renal cell carcinoma.