Overview
Medullary thyroid carcinoma (MTC) is a rare type of thyroid cancer that arises from the parafollicular C‑cells (also called calcitonin‑producing cells) of the thyroid gland. Unlike the more common papillary and follicular thyroid cancers, which originate from follicular cells, MTC produces excess calcitonin and sometimes other hormones such as carcinoembryonic antigen (CEA).
Who it affects: MTC can occur at any age but most commonly presents in adults between 40 and 60 years old. Approximately 25 % of cases are hereditary, occurring as part of multiple endocrine neoplasia type 2 (MEN 2) syndromes, while the remaining 75 % arise sporadically.
Prevalence: In the United States, MTC accounts for about 1–2 % of all thyroid cancers, translating to roughly 2,000 new diagnoses per year. Worldwide incidence is similar, with slight regional variations linked to the prevalence of hereditary MEN 2 mutations.
Symptoms
Early MTC often produces no noticeable signs, which is why routine neck examinations and blood tests for calcitonin are important in high‑risk families. When symptoms do appear, they may include:
- Neck mass or nodule – A painless, firm lump in the front of the neck that may gradually enlarge.
- Hoarseness or voice changes – Occurs if the tumor presses on the recurrent laryngeal nerve.
- Difficulty swallowing (dysphagia) – May indicate local invasion into the esophagus.
- Breathlessness or noisy breathing – Can result from airway compression.
- Pain in the neck, jaw, or ear – Often radiating pain due to nerve involvement.
- Metastatic symptoms – When cancer spreads:
- Bone pain, fractures, or hypercalcemia (high calcium) from bone metastases.
- Persistent cough, chest pain, or shortness of breath if the lungs are involved.
- Abdominal pain, jaundice, or weight loss with liver metastases.
- Hormone‑related signs – Excess calcitonin rarely causes symptoms, but very high levels can lead to:
- Diarrhea.
- Facial flushing.
- Skin itching.
Causes and Risk Factors
Genetic Causes
About one‑quarter of MTC cases are hereditary and result from germline mutations in the RET proto‑oncogene (chromosome 10). These mutations cause continuous activation of a signaling pathway that drives uncontrolled cell growth.
- MEN 2A – Includes MTC, pheochromocytoma, and primary hyperparathyroidism.
- MEN 2B – Includes MTC, pheochromocytoma, mucosal neuromas, and a marfanoid habitus.
- Familial medullary thyroid carcinoma (FMTC) – Isolated MTC without other endocrine tumors.
Non‑genetic (Sporadic) Causes
- Age > 40 (median age ~50 years).
- Male sex has a slightly higher incidence (≈55 % of cases).
- Radiation exposure to the neck (though the link is weaker than for papillary thyroid cancer).
Risk Factors Summary
- Family history of MEN 2 or FMTC.
- Known RET mutation (even if asymptomatic).
- Previous radiation therapy to the head/neck region.
- Being male and over 40 years old.
Diagnosis
Because MTC can be silent, a combination of clinical evaluation, blood tests, imaging, and pathology is used.
Biochemical Screening
- Serum calcitonin – The most sensitive marker; values >10 pg/mL in women or >15 pg/mL in men usually indicate C‑cell activity.
- Carcinoembryonic antigen (CEA) – Often elevated; useful for monitoring disease burden.
Imaging Studies
- Neck ultrasound – First‑line to detect thyroid nodules and cervical lymph nodes.
- Fine‑needle aspiration (FNA) with calcitonin washout – Cytology plus measurement of calcitonin in the needle wash improves diagnostic accuracy.
- Cross‑sectional imaging (CT, MRI) – Evaluates extrathyroidal spread, especially to the mediastinum.
- Functional imaging – ^18F‑DOPA PET/CT or ^68Ga‑DOTATATE PET for detecting distant metastases and for planning targeted radiolabeled therapy.
Genetic Testing
All patients with confirmed MTC should undergo RET genetic testing. The results guide surgical timing, prophylactic surgery in relatives, and eligibility for targeted therapies.
Staging
Staging follows the AJCC (8th edition) TNM system. Key elements include tumor size (T), nodal involvement (N), and distant metastasis (M). Accurate staging determines prognosis and treatment planning.
Treatment Options
Management is multidisciplinary, involving endocrine surgeons, medical oncologists, radiologists, and genetics counselors.
Surgical Treatment
- Total thyroidectomy – Removal of the entire thyroid gland is the standard curative approach.
- Central neck dissection (level VI) – Recommended for all patients because microscopic nodal disease is common.
- Lateral neck dissection – Performed when clinical or imaging evidence shows lateral neck node involvement.
- Prophylactic surgery – In RET‑mutation carriers (especially MEN 2), surgery is often performed before the age of 5 (MEN 2B) or 10 (MEN 2A) to prevent disease.
Targeted Systemic Therapies
When disease is advanced or unresectable, targeted drugs that inhibit RET kinase are preferred.
- Selpercatinib (Retevmo) – FDA‑approved for RET‑fusion positive and RET‑mutated MTC; shown to produce a 69 % overall response rate in the LIBRETTO‑001 trial (NEJM 2020)【1】.
- Lenvatinib (Lenvima) and Vandetanib (Caprelsa) – Multi‑kinase inhibitors with activity against RET; improve progression‑free survival but have more side effects.
Radiation Therapy
- External beam radiation – Considered for residual disease, unresectable neck nodes, or palliation of bone metastases.
- Radioactive iodine (RAI) – Not effective because C‑cells do not take up iodine.
Chemotherapy
Conventional cytotoxic chemotherapy has limited efficacy; it is reserved for rare cases of rapidly progressive disease unresponsive to targeted agents.
Supportive and Lifestyle Measures
- Calcium and vitamin D supplementation if hypoparathyroidism occurs after surgery.
- Management of pheochromocytoma (if present) before thyroid surgery to avoid hypertensive crises.
- Regular monitoring of calcitonin and CEA levels post‑treatment to detect recurrence early.
Living with Medullary Thyroid Carcinoma
Follow‑up Schedule
- First year – Serum calcitonin and CEA every 3 months; neck ultrasound every 6 months.
- Years 2–5 – Labs every 6 months; imaging based on findings.
- Beyond 5 years – Annual labs; imaging if markers rise.
Managing Hormone‑Related Symptoms
If calcitonin‑related diarrhea or flushing occurs, dietary modifications (low‑fat, small frequent meals) and antidiarrheal agents (loperamide) can help.
Psychosocial Support
- Join support groups (e.g., American Thyroid Association patient community).
- Consider counseling for anxiety related to hereditary risk.
- Genetic counseling for family planning.
Activities & Lifestyle
- Regular aerobic exercise is safe after recovery from surgery.
- Avoid smoking and excessive alcohol, which can impair wound healing and increase cardiovascular risk.
- Maintain a balanced diet rich in calcium and vitamin D, especially if parathyroid glands were removed.
Prevention
Because many MTC cases are genetically predetermined, primary prevention is limited, but risk can be reduced through:
- Genetic screening – Family members of a patient should be offered RET testing; carriers can undergo prophylactic thyroidectomy.
- Avoidance of unnecessary neck radiation – Use shielding protocols when radiation is medically required.
- Early detection – Annual physical neck exams and serum calcitonin measurement for high‑risk individuals.
Complications
If left untreated or inadequately managed, MTC can lead to:
- Local invasion – Into the trachea, esophagus, or recurrent laryngeal nerve, causing airway obstruction or dysphonia.
- Regional lymph node metastasis – Occurs in ~70 % of cases at diagnosis.
- Distant metastases – Liver, lungs, and bones are common sites; bone lesions can cause fractures and severe pain.
- Hypercalcitonemia – Extremely high calcitonin can cause flushing, diarrhea, and electrolyte disturbances.
- Secondary cancers – Patients with MEN 2 have increased risk of pheochromocytoma and hyperparathyroidism.
- Post‑surgical hypoparathyroidism – Low calcium levels may require lifelong supplementation.
When to Seek Emergency Care
- Sudden, severe difficulty breathing or choking sensation.
- Rapidly worsening hoarseness accompanied by stridor (high‑pitched breathing).
- Sudden, severe neck or throat pain with swelling.
- Unexplained high‑grade fever (>38.5 °C) with neck pain, suggesting infection of a surgical site.
- Episodes of severe hypertension, pounding headache, palpitations, or sweating (possible pheochromocytoma crisis).
- Rapidly increasing calcium levels causing confusion, muscle weakness, or cardiac arrhythmias.
These signs may indicate airway compromise, infection, or a hormonal emergency that requires immediate treatment.
Sources: Mayo Clinic, National Cancer Institute, American Thyroid Association, FDA prescribing information for selpercatinib, NEJM 2020 (LIBRETTO‑001), CDC thyroid cancer statistics, WHO Cancer Fact Sheets.