Since rabbit CYP4B1 (rCYP4B1), unlike hCYP4B1, is known to activate exogenous protoxins such as 4-IPO 25, resulting in highly toxic compounds (Figure 1c), it has been considered a promising candidate for the clinical application of tumor-killing suicide gene systems [28,29]. The gene discussed is CYP4B1; the disease is neoplasm.