Thyroid Cancer: Causes, Symptoms, Diagnosis and Treatment — Overview, Diagnosis & Treatment Options | MyMedicPlus

Thyroid cancer is the most common endocrine malignancy and the fastest-growing cancer diagnosis by incidence in the United States, with approximately 586,000 new cases globally per year and 44,000 cases in the US annually. The rising incidence is substantially attributable to the incidental detection of small papillary thyroid microcarcinomas on cross-sectional imaging and ultrasound performed for other indications. Four main histological types are recognised based on the cell of origin. Papillary thyroid carcinoma (PTC) is by far the most common, accounting for approximately 85% of cases, arising from follicular cells and typically displaying an indolent course with lymph node metastases but excellent long-term survival. Follicular thyroid carcinoma (FTC, approximately 10%) also arises from follicular cells but spreads haematogenously to bone and lung rather than lymphatically. Medullary thyroid carcinoma (MTC, approximately 2-3%) arises from parafollicular C-cells secreting calcitonin, and is associated with MEN2A and MEN2B syndromes. Anaplastic thyroid carcinoma (ATC, less than 1%) is a dedifferentiated, uniformly fatal malignancy unless BRAF-targeted therapy is applicable. The AJCC 8th Edition staging system substantially revised the PTC/FTC staging by raising the age cut-off from 45 to 55 years, resulting in most young patients with differentiated TC being classified as Stage I-II regardless of lymph node involvement.

Prior ionising radiation exposure — particularly to the head and neck region in childhood — is the strongest established risk factor for differentiated thyroid cancer, especially PTC. Atomic bomb survivors, Chernobyl-affected populations, and patients who received neck irradiation for benign conditions (enlarged thymus, tonsillitis, tinea capitis) in the mid-20th century show markedly elevated thyroid cancer incidence. Therapeutic radiation for childhood cancers also confers elevated risk. Iodine deficiency promotes follicular thyroid carcinoma (FTC) by inducing chronic TSH stimulation, while iodine excess is associated with papillary type. Key molecular alterations drive specific subtypes: BRAF V600E is present in approximately 60% of PTC (associated with worse clinicopathological features including extrathyroidal extension, lymph node metastasis, and higher ATA risk category); RET/PTC rearrangements (RET-CCDC6, RET-NCOA4) are present in 10-20% of PTC, particularly after radiation; RAS mutations (NRAS, HRAS, KRAS) predominate in FTC and follicular adenoma; TERT promoter mutations co-occurring with BRAF or RAS confer the highest risk of aggressive behaviour and mortality in differentiated TC; germline RET mutations cause hereditary MTC (MEN2A: RET codon C634 mutations, MEN2B: RET M918T, highest-risk codon); TP53 mutations characterise the dedifferentiated progression from differentiated to anaplastic carcinoma.

The overwhelming majority of thyroid cancers are detected as an asymptomatic thyroid nodule discovered incidentally on neck ultrasound, CT, or MRI performed for unrelated reasons — so-called 'incidentalomas'. Symptomatic differentiated thyroid cancer may present with a gradually enlarging neck lump, firm thyroid nodule, or palpable ipsilateral cervical lymphadenopathy; the thyroid nodule is typically painless and firm or hard to palpation. Locally advanced PTC or FTC may invade adjacent structures: hoarseness from recurrent laryngeal nerve invasion, dysphagia from oesophageal compression, stridor from tracheal invasion or compression, and fixed immobile thyroid nodule adherent to the underlying musculature. Haematogenous metastases from FTC most commonly affect bone (producing bone pain, pathological fractures) and lung (pulmonary nodules, dyspnoea); cervical lymph node metastases are the predominant pattern in PTC. MTC presents specifically with diarrhoea from calcitonin excess, facial flushing (a serotonin-mediated effect), and in MEN2A, pheochromocytoma and primary hyperparathyroidism symptoms coexist. ATC presents as a dramatically and rapidly enlarging, painful, hard neck mass with compressive symptoms developing over weeks, frequently with vocal cord paralysis, stridor, and superior vena cava syndrome; it is among the most rapidly fatal of all solid malignancies, with a median OS of 3-5 months untreated.

The diagnostic workup for thyroid cancer begins with thyroid ultrasound to characterise nodule features using validated risk stratification systems — the ACR TIRADS or ATA risk stratification system — which classify nodules based on echogenicity, margins, shape, calcification pattern, and vascularity to guide FNA biopsy decisions. Ultrasound-guided fine needle aspiration cytology (FNA) is interpreted using the Bethesda System for Reporting Thyroid Cytopathology (Categories I-VI), with Categories V-VI (suspicious for malignancy and malignant) proceeding to surgery and Category III-IV (atypia of undetermined significance and follicular neoplasm) undergoing molecular testing with ThyroSeq or Afirma genomic classifiers. Serum TSH, thyroglobulin, and calcitonin (for suspected MTC) are baseline biochemical tests. CEA is co-elevated with calcitonin in MTC. BRAF V600E, RAS, TERT promoter, RET, and NTRK mutations detected on surgical pathology or molecular panels guide prognosis (ATA risk stratification) and targeted therapy selection. Post-thyroidectomy: serum thyroglobulin and thyroglobulin antibodies serve as disease markers for differentiated TC surveillance; radioactive iodine (RAI) whole-body scan at 6-12 months post-ablation confirms remnant ablation; neck ultrasound at 6 and 12 months post-surgery detects lymph node recurrence. Neck CT/MRI delineates local invasion for surgical planning in locally advanced disease. Germline RET mutation testing is mandatory for all MTC patients.

Treatment of thyroid cancer is histotype-specific and risk-stratified by the American Thyroid Association (ATA) low, intermediate, and high-risk classification. Differentiated thyroid cancer (PTC/FTC): total thyroidectomy with central neck dissection is recommended for tumours greater than 4 cm, bilateral disease, extrathyroidal extension, or high-risk molecular features (TERT mutation, BRAF V600E with adverse histological features); hemithyroidectomy is acceptable for low-risk tumours less than 4 cm confined to the thyroid without nodal involvement. RAI (iodine-131) ablation at 30-150 mCi is administered 4-6 weeks post-thyroidectomy for ATA intermediate- and high-risk differentiated TC following TSH stimulation (exogenous rhTSH or thyroid hormone withdrawal to raise TSH above 30 mIU/L); RAI is not indicated for ATA low-risk unifocal PTC less than 1 cm. TSH suppression with levothyroxine to achieve TSH below 0.1 mIU/L is maintained for high-risk differentiated TC during active surveillance. RAI-refractory differentiated TC: lenvatinib (SELECT trial) or sorafenib (DECISION trial) as first-line VEGFR-targeted TKI therapy; cabozantinib as second-line. MTC treatment: total thyroidectomy plus central compartment lymph node dissection; selpercatinib (RET-selective inhibitor) is FDA-approved for RET-mutated advanced MTC with a 69% objective response rate (LIBRETTO-001 trial); cabozantinib and vandetanib for unselected advanced MTC. ATC with BRAF V600E: dabrafenib plus trametinib (BRAF + MEK inhibition) achieves approximately 56% ORR and is FDA-approved — a dramatic improvement over historical outcomes; BRAF wild-type ATC: multidisciplinary approach including surgery, intensity-modulated radiotherapy, and clinical trial participation.

The most effective preventive measures for thyroid cancer focus on avoiding ionising radiation exposure and managing hereditary risk through genetic testing and prophylactic surgery. Radiation exposure to the neck should be minimised: shielding of the thyroid gland during dental and chest X-rays, and minimising radiological imaging studies involving the neck in children and young adults, are routine measures. Following nuclear accidents, potassium iodide (KI) tablets distributed to nearby populations saturate the thyroid gland with stable iodine, blocking uptake of radioactive iodine (131I) from fallout, thereby reducing radiation-induced thyroid cancer risk; this is an established public health emergency measure endorsed by the WHO and CDC. Hereditary MTC (MEN2A and MEN2B): germline RET mutation testing is offered to all first-degree relatives of MTC patients, as RET mutations are transmitted in an autosomal dominant pattern with high penetrance. Prophylactic total thyroidectomy is recommended for RET M918T (MEN2B, highest-risk) carriers in the first months of life; for C634 (MEN2A, high-risk) carriers before age 5 years; and for lower-risk RET codon carriers at 5-10 years of age, per the ATA Hereditary MTC Guidelines. Iodine supplementation in iodine-deficient populations through universal salt iodisation programmes reduces the incidence of FTC. Active surveillance (watchful waiting with serial ultrasound rather than immediate surgery) for low-risk papillary thyroid microcarcinomas (less than 1 cm, no high-risk features) is an accepted approach endorsed by ATA guidelines to avoid overtreatment.

Seek prompt evaluation for any new or growing neck lump, particularly one that is firm or hard on palpation, as all thyroid nodules require initial evaluation with thyroid ultrasound and TSH measurement. The finding of a thyroid nodule on any imaging modality (CT, MRI, PET) performed for another reason should be followed up with dedicated thyroid ultrasound and ATA risk stratification to determine whether FNA biopsy is indicated. Hoarseness that develops progressively — particularly in the absence of a respiratory infection — may indicate recurrent laryngeal nerve involvement by thyroid cancer and warrants urgent thyroid ultrasound and ENT referral. Dysphagia, stridor, or progressive breathing difficulty associated with a thyroid enlargement represents a medical urgency requiring same-day evaluation. Any patient with a personal or family history of MEN2A, MEN2B, or RET mutation should be under regular thyroid ultrasound surveillance and must report any new or growing neck mass immediately. A rapidly enlarging, painful thyroid mass with systemic symptoms (fever, weight loss) in an adult older than 60 years raises the possibility of anaplastic thyroid carcinoma — a medical emergency requiring urgent CT and multidisciplinary evaluation within days, not weeks. All patients with known thyroid cancer should adhere to their scheduled thyroglobulin monitoring and neck ultrasound surveillance, reporting any new neck symptoms between appointments.

PTC Stage I/II (most patients under 55 years): 5-year OS essentially 100%. Stage III/IV differentiated TC: 5-year OS approximately 50-85% depending on extent. MTC with distant metastasis: 10-year OS approximately 25%. ATC: historically median OS 3-5 months; BRAF V600E-positive ATC treated with dabrafenib plus trametinib shows objective response rates of approximately 56% with some durable responses, transforming outcomes for this previously lethal subtype. Selpercatinib has revolutionised outcomes for RET-mutated MTC. The prognosis for Thyroid Cancer: Causes, Symptoms, Diagnosis and Treatment varies depending on severity at diagnosis, the patient's overall health, and how promptly treatment is initiated. With early diagnosis and appropriate management, many patients achieve good outcomes and maintain quality of life. Regular follow-up with healthcare providers is essential to monitor progress, adjust treatment as needed, and detect any complications early. Adherence to prescribed treatments and lifestyle modifications significantly improves long-term prognosis.