Thyroid Disorders · Pathology

A patient is found to have a thyroid mass and an elevated serum calcitonin level. Biopsy shows an amyloid-rich stroma. What is the most likely diagnosis?

  1. Papillary carcinoma
  2. Follicular carcinoma
  3. Medullary carcinoma
  4. Anaplastic carcinoma
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Correct answer: Medullary carcinoma

In medullary thyroid carcinoma, the neoplastic C cells secrete procalcitonin, which can deposit in the tumor stroma as amyloid. This amyloid stains positive with Congo red and shows apple-green birefringence under polarized light.

Difficulty: Medium Question 8 of 20

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