Thyroid cancer develops in the thyroid gland, a butterfly-shaped endocrine gland located at the base of the neck that produces hormones regulating metabolism. The American Cancer Society estimates approximately 43,720 new cases of thyroid cancer are diagnosed in the United States each year, with roughly 2,120 deaths. Thyroid cancer is the most rapidly increasing cancer in the U.S. by incidence, largely due to increased detection of small papillary tumors through imaging. It is approximately three times more common in women than men.
The prognosis for most thyroid cancers is excellent. Differentiated thyroid cancers (papillary and follicular) have five-year survival rates exceeding 98% when treated appropriately. However, anaplastic thyroid cancer remains one of the most lethal human malignancies, and medullary thyroid cancer requires a distinct treatment approach.
Types of Thyroid Cancer
Papillary Thyroid Cancer (PTC)
The most common type, accounting for approximately 80% of all thyroid cancers. Papillary thyroid cancer arises from thyroid follicular cells and typically grows slowly. It often spreads to cervical lymph nodes but rarely to distant sites. BRAF V600E mutations are found in approximately 40–60% of PTCs and are associated with more aggressive behavior. Despite frequent lymph node involvement, the prognosis remains excellent, with disease-specific mortality under 2% at 20 years for most patients.
Follicular Thyroid Cancer (FTC)
The second most common type, representing approximately 10–15% of thyroid cancers. Follicular thyroid cancer also arises from follicular cells but is more likely to spread hematogenously to distant sites (lungs, bones) rather than to lymph nodes. RAS mutations are common in FTC. Hürthle cell carcinoma (oncocytic carcinoma) is a variant that may be more aggressive and less responsive to radioactive iodine.
Medullary Thyroid Cancer (MTC)
Accounts for approximately 3–5% of thyroid cancers and arises from the parafollicular C cells that produce calcitonin. Approximately 25% of MTC cases are hereditary, associated with RET proto-oncogene mutations in the context of multiple endocrine neoplasia type 2 (MEN2A, MEN2B) or familial MTC. Calcitonin and carcinoembryonic antigen (CEA) serve as serum tumor markers. MTC does not respond to radioactive iodine therapy.
Anaplastic Thyroid Cancer (ATC)
The rarest and most aggressive type, accounting for 1–2% of thyroid cancers. Anaplastic thyroid cancer is an undifferentiated malignancy that grows extremely rapidly and has a median survival of approximately 5 months. It often arises from a pre-existing differentiated thyroid cancer. The combination of dabrafenib and trametinib for BRAF V600E–mutant ATC represents a significant treatment advance, with dramatic responses reported in approximately 60% of patients.
Risk Factors
- Radiation exposure — Childhood head and neck radiation is the best-established environmental risk factor. Survivors of the Chernobyl nuclear disaster showed dramatically increased papillary thyroid cancer rates.
- Gender — Women are approximately 3 times more likely to develop thyroid cancer than men.
- Family history and genetics — RET mutations (MEN2 syndromes), PTEN hamartoma tumor syndrome (Cowden disease), familial adenomatous polyposis (FAP), and Carney complex all increase risk.
- Iodine deficiency — Associated with increased risk of follicular thyroid cancer.
- Age — Thyroid cancer can occur at any age but is most commonly diagnosed between ages 25 and 65.
- Obesity — Higher BMI is associated with increased thyroid cancer risk.
Thyroid Cancer Staging
Staging for differentiated thyroid cancer (papillary and follicular) uniquely incorporates patient age. Patients under 55 years of age can be classified as stage I or II only, reflecting the excellent prognosis in younger patients regardless of disease extent.
| Stage | Description | 5-Year Survival Rate |
|---|---|---|
| Stage I (age <55) | Any T, any N, no distant metastasis | ~99–100% |
| Stage II (age <55) | Any T, any N, with distant metastasis | ~95%+ |
| Stage I (age ≥55) | Tumor ≤4 cm confined to thyroid, no nodes, no distant metastasis | ~99–100% |
| Stage II (age ≥55) | Tumor >4 cm or minor extrathyroidal extension, or any tumor with N1 nodes | ~95–98% |
| Stage III (age ≥55) | Gross extrathyroidal extension into subcutaneous tissue, larynx, trachea, esophagus, or recurrent laryngeal nerve | ~90–95% |
| Stage IV (age ≥55) | Invasion of prevertebral fascia, encasement of carotid artery/mediastinal vessels, or distant metastasis | ~50–78% |
Staging based on AJCC 8th Edition. Anaplastic thyroid cancer is automatically classified as Stage IV regardless of extent. Survival rates from SEER data.
Treatment Options
Surgery
Surgery is the primary treatment for nearly all thyroid cancers:
- Total thyroidectomy — Removal of the entire thyroid gland. Recommended for tumors >1 cm, bilateral disease, extrathyroidal extension, lymph node metastases, or when radioactive iodine therapy is planned.
- Thyroid lobectomy — Removal of one thyroid lobe. Appropriate for small (≤1 cm), low-risk, unilateral papillary cancers without concerning features. Avoids the need for lifelong thyroid hormone replacement in some patients.
- Central and lateral neck dissection — Performed when cervical lymph nodes are clinically involved or suspicious on preoperative imaging.
Radioactive Iodine (RAI) Therapy
Radioactive iodine (I-131) is a key adjuvant treatment for differentiated thyroid cancers (papillary and follicular). Thyroid follicular cells concentrate iodine, and after thyroidectomy, RAI selectively targets and destroys residual thyroid tissue and iodine-avid metastases. RAI is recommended for intermediate- and high-risk patients but is generally not necessary for very low-risk papillary microcarcinomas. TSH stimulation (via thyroid hormone withdrawal or recombinant TSH injection) enhances RAI uptake.
External Beam Radiation Therapy
External beam radiation is not a primary treatment for differentiated thyroid cancer but may be used for anaplastic thyroid cancer, unresectable or locally recurrent disease, and selected cases of medullary thyroid cancer with positive surgical margins or extranodal extension.
TSH Suppression Therapy
Levothyroxine (thyroid hormone replacement) is administered at doses sufficient to suppress TSH, which can stimulate thyroid cancer growth. The degree of suppression is tailored to risk: high-risk patients target TSH below 0.1 mU/L, while low-risk patients in remission can allow TSH in the low-normal range (0.5–2.0 mU/L).
Targeted Therapy
For radioactive iodine–refractory differentiated thyroid cancer and advanced medullary thyroid cancer, several targeted therapies are available:
- Lenvatinib (Lenvima) and sorafenib (Nexavar) — Multi-kinase inhibitors approved for RAI-refractory differentiated thyroid cancer.
- Cabozantinib (Cabometyx) and vandetanib (Caprelsa) — Approved for progressive medullary thyroid cancer.
- Selpercatinib (Retevmo) and pralsetinib (Gavreto) — Highly selective RET inhibitors approved for RET-mutant medullary thyroid cancer and RET fusion–positive thyroid cancer.
- Dabrafenib + trametinib — BRAF/MEK inhibitor combination approved for BRAF V600E–mutant anaplastic thyroid cancer, showing remarkable responses in this otherwise lethal disease.
Follow-Up and Monitoring
Long-term surveillance is essential for thyroid cancer patients, as recurrences can occur years or even decades after initial treatment. Monitoring typically includes:
- Thyroglobulin (Tg) measurement — Serum thyroglobulin serves as a highly sensitive tumor marker for differentiated thyroid cancer after total thyroidectomy and RAI ablation. Detectable or rising Tg levels in the absence of anti-Tg antibodies suggest recurrent disease.
- Neck ultrasound — Regular cervical ultrasound to detect local recurrence or lymph node metastases. Fine-needle aspiration (FNA) with Tg washout measurement can confirm suspicious nodes.
- Diagnostic whole-body iodine scan — Used selectively in intermediate- and high-risk patients to detect iodine-avid residual or recurrent disease.
- Calcitonin and CEA monitoring — Essential for medullary thyroid cancer follow-up. Rising calcitonin or CEA doubling times correlate with disease progression.