Medullary thyroid cancer is an uncommon type of thyroid cancer that develops from parafollicular C cells, which produce the hormone calcitonin. Unlike other thyroid cancers, it can be associated with inherited genetic changes, particularly mutations in the RET gene. Some cases occur without a family history.
Medullary thyroid cancer (MTC) originates in the C cells of the thyroid gland, located at the front of the neck. These cells produce calcitonin, a hormone involved in calcium regulation. MTC differs from more common thyroid cancers because it arises from a different type of cell and has a strong association with specific genetic changes. Approximately one-quarter of cases are hereditary, while the remaining cases occur sporadically. Identifying whether the cancer is inherited is important because it can influence medical management and help relatives understand their potential risk.
The RET gene plays a central role in hereditary medullary thyroid cancer. Certain inherited changes in this gene can cause abnormal cellular signaling, contributing to the development of cancer in thyroid C cells. Hereditary MTC is commonly associated with multiple endocrine neoplasia type 2 (MEN2), a genetic syndrome that can affect several endocrine glands.
MEN2 is generally divided into MEN2A and MEN2B. Both conditions are associated with an increased risk of medullary thyroid cancer, although their additional features can differ. A person with hereditary MTC may inherit a pathogenic RET variant from a parent, and each child of an affected individual with an autosomal dominant RET variant generally has a 50 percent chance of inheriting it.
Important genetic and hereditary factors include:
RET gene mutations: These changes are the primary known genetic cause of hereditary MTC and can lead to abnormal cell growth.
Multiple endocrine neoplasia type 2A: This condition is associated with MTC and may also involve pheochromocytoma, a tumor of the adrenal glands, and parathyroid gland abnormalities.
Multiple endocrine neoplasia type 2B: This syndrome is associated with a high risk of MTC and may include pheochromocytoma, distinctive physical features, and benign growths involving nerve tissue.
Familial medullary thyroid cancer: This refers to families in which MTC occurs due to inherited RET variants, sometimes without other characteristic MEN2 features.
Sporadic MTC: These cases occur without an identified inherited predisposition, although genetic changes can still be present within the tumor itself.
Medullary thyroid cancer may initially develop without noticeable symptoms. As the tumor grows, a person may experience a lump in the neck, difficulty swallowing, hoarseness, or enlarged lymph nodes. Advanced disease can sometimes cause diarrhea or flushing because certain tumors produce biologically active substances.
Diagnosis generally involves a physical examination, thyroid imaging, laboratory testing, and examination of cells or tissue when indicated. Blood calcitonin and carcinoembryonic antigen (CEA) measurements can help evaluate the disease and monitor its course. Genetic counseling and germline RET testing are important for people diagnosed with MTC, even when there is no known family history, because an inherited variant may have implications for relatives.
Common approaches to evaluation and management include:
Ultrasound examination: Imaging helps assess thyroid nodules and nearby lymph nodes.
Blood testing: Calcitonin and CEA levels can provide useful information about tumor activity and follow-up.
Genetic testing: RET testing can identify hereditary disease and help determine whether relatives should receive testing.
Surgical treatment: Thyroidectomy, sometimes combined with lymph node removal, is a principal treatment for localized MTC. The surgical approach depends on disease extent and individual circumstances.
Ongoing monitoring: Follow-up commonly includes calcitonin and CEA measurements, with additional imaging when appropriate.
Targeted therapies: For advanced or progressive disease, certain medicines that target RET or other relevant pathways may be considered, depending on the tumor's molecular characteristics and clinical circumstances.
Understanding genetic conditions associated with medullary thyroid cancer supports informed medical decisions and appropriate family evaluation. Individuals with a confirmed RET variant should receive guidance from qualified healthcare professionals about surveillance, treatment options, and testing for at-risk relatives. Early identification of hereditary risk can be particularly important because preventive or early interventions may be appropriate for some family members before cancer develops.