A 52-year-old woman from Mumbai presents with a rapidly enlarging thyroid mass, dysphagia, and stridor. Fine-needle aspiration cytology (FNAC) shows numerous atypical cells with high mitotic activity. Regarding anaplastic thyroid carcinoma (ATC), all of the following are characteristic features EXCEPT:
A. TP53 mutations and BRAF V600E alterations are among the most common genetic abnormalities, with TP53 being present in >70% of cases
B. It demonstrates excellent response to radioactive iodine ablation due to retained iodine-concentrating capacity and high metabolic activity
C. Median survival is approximately 3–6 months from diagnosis, with most patients dying within 1 year despite multimodal therapy
D. It is derived from differentiated thyroid cancer in approximately 20–30% of cases, often representing dedifferentiation of pre-existing papillary or follicular carcinoma
Anaplastic thyroid carcinoma is the most aggressive thyroid malignancy, characterized by rapid growth, early distant metastases, and uniformly poor prognosis. It does NOT respond to radioactive iodine because it loses the ability to concentrate iodine.
Epidemiology & Origin
Table
Feature
Details
Frequency
1–2% of thyroid cancers
Age of onset
Typically >60 years
Origin
20–30% arise from pre-existing differentiated cancer (PTC or FTC)
Dedifferentiation
Often represents transformation of indolent tumors to aggressive phenotype
High-YieldNEET PG
ATC can arise de novo or from dedifferentiation of papillary or follicular carcinoma. The transition is marked by loss of thyroglobulin production and iodine-concentrating capacity.
Molecular Genetics
1.
Most Common Alterations
TP53 mutations: Present in >70% of cases (tumor suppressor loss)
BRAF V600E: Found in 25–40% of cases
RAS mutations: Present in 20–30% of cases
PTEN loss: Frequent (loss of phosphatase and tensin homolog)
PI3K/AKT pathway activation: Common
Mnemonic: "TP53 BRAF RAS PTEN" — the four major drivers of ATC transformation.
Loss of Differentiation = Loss of Iodine Uptake
1.
Why ATC Does NOT Respond to Radioactive Iodine
Anaplastic cells lose expression of the sodium-iodide symporter (NIS)
No thyroglobulin production
Cannot concentrate radioactive iodine
RAI scan shows "cold" nodule (no uptake)
RAI therapy is ineffective
Clinical Pearl
A thyroid mass that is "cold" on RAI scan (no uptake) is more likely to be anaplastic or poorly differentiated. In contrast, papillary and follicular carcinomas retain iodine-concentrating capacity and show uptake on RAI scan.
Clinical Behavior & Prognosis
1.
Aggressive Features
Rapid growth (weeks to months)
Early invasion of surrounding structures (trachea, esophagus, laryngeal nerve)
Distant metastases at presentation in 50% of cases
Lung (80%), bone (15%), brain (10%)
2.
Dismal Prognosis
Median survival: 3–6 months from diagnosis
1-year survival: <20% even with multimodal therapy
5-year survival: <5%
Treatment Approach
Surgery: Attempted if resectable for airway protection; rarely curative
Targeted therapy: BRAF inhibitors (dabrafenib) + MEK inhibitors (trametinib) for BRAF-mutant ATC; emerging role
Immunotherapy: Checkpoint inhibitors (pembrolizumab) under investigation
Radioactive iodine: NOT effective (no iodine uptake)
Warning
ATC responds well to RAI — FALSE. This is a critical trap. ATC loses differentiation and therefore loses the ability to concentrate iodine. RAI is contraindicated in ATC.
Why Option 3 is Incorrect
Option 3 claims ATC demonstrates "excellent response to radioactive iodine ablation due to retained iodine-concentrating capacity." This is fundamentally wrong:
ATC cells are undifferentiated and lose NIS expression
They do NOT concentrate iodine
RAI is ineffective and not used in ATC
This describes papillary or follicular carcinoma, not anaplastic carcinoma
Robbins 10e Ch 24
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