The CYP1B1 V432L polymorphism has a much more drastic effect on cell phenotype than the level of expression of CYP1B1 by itself: the cells infected with the variant form of CYP1B1 strongly differ from the other isogenic cells, in terms of cell proliferation, motility, invasiveness and chemosensitivity, and of tumour growth and drug sensitivity after in vivo transplantation. The gene discussed is CYP1B1; the disease is neoplasm.