anaplastic thyroid carcinoma
Summary
Anaplastic thyroid carcinoma is a rare, highly aggressive, undifferentiated thyroid malignancy typically occurring in elderly patients, often arising from dedifferentiation of pre-existing differentiated thyroid cancer (papillary or follicular) or long-standing goiter. It presents as a rapidly enlarging neck mass causing compressive symptoms (dysphagia, dyspnea, hoarseness) and carries an extremely poor prognosis, with median survival of only 3-6 months.
Detail
Anaplastic thyroid carcinoma (ATC) accounts for <2% of thyroid cancers but causes a disproportionate share of thyroid cancer deaths due to its aggressive behavior. It typically arises in patients >60 years old, often with a history of multinodular goiter or pre-existing differentiated thyroid carcinoma (papillary or follicular), suggesting a dedifferentiation pathway. Molecularly, ATC is associated with mutations in TP53, and often shows accumulation of mutations found in differentiated cancers (BRAF, RAS) plus additional alterations (TP53, TERT promoter, PIK3CA, beta-catenin).
Clinically, patients present with a rapidly growing, firm, fixed neck mass that invades local structures, causing dysphagia, dyspnea, stridor, hoarseness (recurrent laryngeal nerve involvement), and neck pain. Lymphadenopathy and distant metastases (lung, bone) are common at diagnosis. On histology, tumor cells are highly pleomorphic, undifferentiated, with numerous mitoses and necrosis; they lose the ability to take up iodine or produce thyroglobulin, making radioactive iodine therapy ineffective.
Diagnosis is via fine-needle aspiration or core biopsy showing undifferentiated cells; immunohistochemistry may show loss of thyroid-specific markers (thyroglobulin, TTF-1) but can retain PAX8 positivity in some cases, helping distinguish from other anaplastic malignancies (e.g., lymphoma, sarcoma).
Management is largely palliative given rapid progression; options include surgery (if resectable), external beam radiation, and chemotherapy, though response is often poor. Newer targeted therapies (BRAF/MEK inhibitors like dabrafenib/trametinib for BRAF V600E-mutant tumors) have improved outcomes in a subset of patients. Prognosis remains dismal, with median survival of 3-6 months and 1-year survival <20%, making this one of the most lethal human cancers.
Key boards points: distinguish from more indolent papillary/follicular thyroid carcinoma; associate with elderly patients and rapid growth; know it does NOT concentrate iodine (RAI therapy ineffective); recognize TP53 mutation association; contrast with medullary thyroid carcinoma (from parafollicular C cells, associated with MEN2, calcitonin-secreting).
Sources
- Robbins and Cotran Pathologic Basis of Disease
- UpToDate: Anaplastic thyroid carcinoma
- First Aid for the USMLE Step 1
- Sabiston Textbook of Surgery
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