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Pathology
Papillary thyroid cancer (PTC)
Develops from thyroid follicular cells
Usually found in 1 lobe; only 10–20% appear in both lobes
Lymph node metastases are more frequent than distant metastases
Mutations in BRAF V600E (T1799A) occurs in 6–80% of patients
Recently, encapsulated noninvasive (ie, no signs of vascular or tumor capsule invasiveness) follicular variants of PTC have been reclassified as a benign entity and renamed “noninvasive follicular thyroid neoplasms with papillary-like nuclear features,” thereby significantly reducing the number of patients who are considered to have thyroid cancer
Nikiforov YE et al. JAMA Oncol 2016;2:1023–1029
Follicular thyroid cancer (FTC)
Develops from the follicular cells in the normal thyroid
Mutations of codon 61 of N-RAS (N2) have been reported in as many as 19% of FTCs. Distant metastases are more frequent than lymph node metastases, namely in FTC with extensive vascular invasion (up to 46%)
Grani G et al. Lancet Diabetes Endocrinol 2018;6:500–514
Hürthle cell carcinoma
Usually assumed to be a variant of FTC, has been recognized as a separate entity in the last WHO classification
Both lymph node and distant metastases are frequent in Hürthle cell carcinoma
Medullary thyroid cancer (MTC)
Accounts for <5% of thyroid cancers
Develops in the C cells of the thyroid
Occurs in a familial form as multiple endocrine neoplasia type 2 (MEN 2A and MEN 2B2) and as a sporadic form (~80% of cases)
Germline mutations in the RET (REarranged during Transfection) ...