I. PAPILLARY CARCINOMA
A. Most common type of thyroid carcinoma (80% of cases)
B. Exposure to ionizing radiation in childhood is a major risk factor.
C. Comprised of papillae lined by cells with clear, ‘Orphan Annie eye’ nuclei and
papillae are often associated with psammoma bodies
D. Often spreads to cervical (neck) lymph nodes, but prognosis is excellent (10-year
2. FOLLICULAR CARCINOMA
A. Malignant proliferation of follicles surrounded by a fibrous capsule with invasion
through the capsule
1. Invasion through the capsule helps distinguish follicular carcinoma from
2. Entire capsule must be examined microscopically.
3. FNA only examines cells and not the capsule; hence, a distinction between
follicular adenoma and follicular carcinoma cannot be made by FNA.
B. Metastasis generally occurs
3. MEDULLARY CARCINOMA
A. Malignant proliferation of parafollicular C cells; comprises 5% of thyroid
1. C cells are neuroendocrine cells that secrete calcitonin.
2. Calcitonin lowers serum calcium by increasing renal calcium excretion but is
inactive at normal physiologic levels.
3. High levels of calcitonin produced by tumor may lead to hypocalcemia.
4. Calcitonin often deposits within the tumor as amyloid.
B. Biopsy reveals sheets of malignant cells in an amyloid stroma
C. Familial cases are often due to multiple endocrine neoplasia (MEN) 2A and 2B,
which are associated with mutations in the RET oncogene.
1. MEN 2 results in medullary carcinoma, pheochromocytoma, and parathyroid
adenomas (2A) or ganglioneuromas of the oral mucosa (2B).
2. Detection of the RET mutation warrants prophylactic thyroidectomy.
VI. ANAPLASTIC CARCINOMA
A. Undifferentiated malignant tumor of the thyroid ,usually seen in elderly
B. Often invades local structures, leading to dysphagia or respiratory compromise
C. Poor prognosis