The European Society of Medical Oncology (ESMO) and National Comprehensive Cancer Network (NCCN) suggest that germline testing for RET mutations is indicated for patients with a family history of RET gene mutations or hereditary MTC, patients with clinical features suspicious for multiple endocrine neoplasia type II, and newly diagnosed patients with clinically apparent sporadic MTC. The gene discussed is RET; the disease is medullary thyroid gland carcinoma.