A 70-year-old man presents with a rapidly enlarging thyroid mass over 3 months, hoarseness and dysphagia. Core needle biopsy shows spindle cells, pleomorphic giant cells and marked mitotic activity consistent with anaplastic thyroid carcinoma. CT chest shows no distant metastases but the tumor encases the carotid artery. According to the AJCC eighth edition TNM staging, which T category does encasement of the carotid artery by anaplastic thyroid carcinoma represent?
- A T3b
- B T4a
- C TX
- D T4b ✓
Correct answer: D. T4b
Explanation
All anaplastic thyroid carcinomas are staged as T4 and there is no T1, T2 or T3 category. T4a refers to gross extrathyroidal extension involving subcutaneous soft tissues, larynx, trachea, esophagus or recurrent laryngeal nerve. T4b refers to gross extrathyroidal extension involving the prevertebral fascia or encasing the carotid artery or mediastinal vessels, which renders the tumor unresectable. Encasement of the carotid artery therefore classifies the tumor as T4b, which is stage IVB if no distant metastases are present.
Reference: AJCC Cancer Staging Manual, 8th ed.
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