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

Anaplastic thyroid carcinoma (ATC) is the rarest but most aggressive thyroid malignancy, accounting for less than 1% of thyroid cancers but approximately 40-50% of thyroid cancer deaths. By AJCC definition, all ATC is classified as Stage IVA, IVB, or IVC at diagnosis. It typically arises by dedifferentiation from pre-existing well-differentiated thyroid cancer.

ATC develops by dedifferentiation from papillary or follicular thyroid cancer, accumulating additional mutations. Key molecular drivers: TP53 mutations (approximately 70%), BRAF V600E (approximately 25-40%), RAS mutations, TERT promoter mutations, and PI3K/mTOR pathway alterations. Risk factors include older age, female sex, long-standing goiter, and prior history of differentiated thyroid cancer.

Rapidly enlarging, painful anterior neck mass developing over weeks — the hallmark presentation. Dyspnea and stridor (tracheal compression), dysphagia (esophageal compression), hoarseness (recurrent laryngeal nerve invasion), and superior vena cava syndrome in advanced disease. Distant metastases (lung, brain, bone) may be present at diagnosis. Constitutional symptoms: fever, weight loss.

CT neck and chest with contrast as urgent priority (airway assessment). PET/CT for complete staging. Core needle or open biopsy for histological diagnosis (large pleomorphic undifferentiated cells with high mitotic rate). Comprehensive molecular profiling: BRAF V600E, RAS, NTRK, ALK, RET mutation testing is essential and urgent as it determines eligibility for targeted therapy. TSH, thyroglobulin usually not elevated.

BRAF V600E mutation positive (approximately 25-40% of ATC): dabrafenib plus trametinib (FDA-approved 2018) — objective response rate approximately 56%, with some complete responses enabling subsequent curative resection. BRAF wild-type: lenvatinib-based regimens or clinical trial enrollment. Resectable disease: complete surgical resection plus adjuvant IMRT plus systemic therapy. Tracheostomy for impending airway compromise. Pembrolizumab combination studies ongoing.

Historical median OS: 3-5 months; 5-year OS less than 5%. BRAF V600E-positive ATC treated with dabrafenib plus trametinib: median OS approximately 14 months, with some patients achieving durable complete responses and potential long-term cure — a transformative advance. Urgent multidisciplinary evaluation at a specialized thyroid oncology center within 24-48 hours of diagnosis is imperative.