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Pathology
Papillary thyroid cancer (PTC)
Develops from the follicular cells in the normal thyroid
Usually found in 1 lobe; only 10–20% appear in both lobes
Considered a differentiated thyroid cancer
Together with follicular thyroid cancer, accounts for 80–90% of all thyroid cancers
Mutations in BRAF have been reported in 60–80% of patients with V600E (T1799A), the most common mutation
Follicular thyroid cancer (FTC)
Less common than PTC
Develops from the follicular cells in the normal thyroid
Considered a differentiated thyroid cancer
Together with PTC, accounts for 80–90% of all thyroid cancers
Hürthle cell carcinoma is usually assumed to be a variant of FTC, although its prognosis is worse
Mutations of codon 61 of N-RAS (N2) have been reported in as many as 19% of follicular tumors
Medullary thyroid cancer (MTC)
Accounts for 5–10% of thyroid cancers
Develops in the C cells of the thyroid; has very little, if any, similarity to normal thyroid tissue
Occurs with multiple endocrine neoplasia type 2 (MEN 2A and MEN 2B2), in familial medullary thyroid carcinoma (FMTC) and as a sporadic form (≈80% of cases are sporadic)
Germline mutations in the RET (REarranged during Transfection) protooncogene cause hereditary MTC (MEN 2A, MEN 2B, and FMTC). In addition, up to 50% of patients with sporadic MTC have somatic RET mutations
MEN 2B: RET mutations in codons 918, 883, or compound heterozygotes (V804M + ...