However, in order to further support this conclusion, it will be important to monitor the marker enzyme activity of CYP3A4 in patients with the medullary thyroid cancer that have been shown to differ in their response to vandetanib and to correlate the phenotypic activity of CYP3A4 to clinical data that shows the patient’s responses to vandetanib treatment. The gene discussed is CYP3A4; the disease is medullary thyroid gland carcinoma.