CYP3A4 causes the oxidation of compounds that are usually used as chemotherapeutic agents for the treatment of osteosarcomas such as etoposide, ifosfamide, cyclophosphamide and doxorubicin, suggesting that the response to these drugs could be worse in tumors with high CYP3A expression, increasing the risk of metastasis. The gene discussed is CYP3A4; the disease is osteosarcoma.