Thyroid gland
Thyroid cancer
Practical molecular pathology

Author: Andrey Bychkov, M.D., Ph.D. (see Authors page)

Revised: 24 February 2017, last major update September 2016

Copyright: (c) 2016-2017, PathologyOutlines.com, Inc.

PubMed Search: molecular pathology thyroid cancer

See also Basics of molecular pathology, Molecular testing in FNA
Cite this page: Practical molecular pathology. PathologyOutlines.com website. http://pathologyoutlines.com/topic/thyroidcancerpracticalmolecpath.html. Accessed June 24th, 2017.
Definition / general
  • Thyroid cancer is a genetically simple disease with a relatively low number of mutations in each tumor
  • Driver mutations and gene fusions are identified in over 90% of thyroid cancers, making it one of the best molecular characterized malignancies in humans
  • MAPK and PI3K-AKT are 2 main signaling pathways involved in the development of thyroid tumors
    • MAPK pathway: activated through point mutations of BRAF or RAS genes and RET / PTC rearrangements; primarily involved in papillary carcinoma
    • PI3K-AKT pathway: activated through point mutations in RAS, PIK3CA, AKT1 and PTEN; primarily involved in follicular carcinoma
    • Simultaneous activation of both pathways becomes more frequent as the tumor grade increases
  • Collectively, the most common alterations are BRAF and RAS point mutations and RET / PTC and PAX8 / PPARγ chromosomal rearrangements
  • Driver gene aberrations in well differentiated thyroid cancer are mutually exclusive (median = 1 mutation per tumor)
  • Dedifferentiated cancers accumulate additional genetic alterations, so called late events (median = 6 mutations per tumor)
  • Chromosomal rearrangements (and resultant gene fusions) are associated with radiation
  • Most somatic mutations are not thyroid specific and are commonly found in various solid cancers
  • Molecular techniques are typically applied to cytological smears, formalin fixed paraffin embedded and snap frozen tissue, see details on Molecular pathology basics page
    • Mutations are detected with real time PCR and DNA sequencing
    • Chromosomal rearrangements are detected with FISH and RT-PCR
    • Immunohistochemistry is specific for detecting mutant proteins (BRAF V600E, NRAS Q61R)
Diagrams / tables

Images hosted on other servers:

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Progress in identifying
mutational markers
in thyroid cancer

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Gene mutations in thyroid tumors

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Genomic landscape of PTC

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Gene fusions in PTC


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BRAF mutation and iodine uptake

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BRAF V600E and tumor recurrence

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TERT mutations

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Drug targets in thyroid cancer

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Drug targets in thyroid cancer

Uses by pathologists
  • Preoperative diagnosis of thyroid nodules with indeterminate FNA
  • Potential prognostic value to predict aggressive disease
  • Targeted therapy
Summary on Key Mutations within Tumor Type
  • Follicular adenoma (FA)
    • RAS 20 - 40%
    • PAX8 / PPARγ 5 - 20%
    • No RET / PTC translocations, BRAF V600E mutation, PTEN mutations (except germline mutations in Cowden syndrome) or PIK3CA / AKT pathway mutations
  • Hyalinizing trabecular tumor
    • Although early reports found RET / PTC somatic translocations with similar frequency as PTC, this was not confirmed with more robust techniques
    • Absence / extreme rarity of BRAF and RAS mutations
  • Follicular thyroid carcinoma (FTC)
    • Mutually exclusive RAS point mutations or PAX8 / PPARγ rearrangements in 75%
    • RAS 30 - 50%
    • PAX8 / PPARγ 30 - 35%
    • TERT 10 - 20%
    • PTEN < 10%
    • PIK3CA 5 - 10%
  • Hürthle cell carcinoma (oncocytic variant of FTC)
    • Alteration of mitochondrial DNA, including deletions, frameshift and missense point mutations
    • Lower prevalence of mutations associated with nononcocytic FTC (RAS, PAX8 / PPARγ)
    • GRIM19 mutations 10 - 20%
    • RAS 10 - 20%
    • PAX8 / PPARγ 5 - 15%, associated with follicular architecture
    • TERT 15 - 20%
    • TP53 up to 20%
    • RET / PTC 35%, all with solid pattern of growth (based on one study)
  • Papillary thyroid carcinoma (PTC)
    • Mutually exclusive genetic events found in 75 - 90% cases: point mutations in BRAF and RAS, rearrangements of RET and NTRK1
    • BRAF 40 - 50%
    • RAS 10 - 20%
    • RET / PTC 5 - 20%
    • TERT 5 - 10%
    • NTRK 5%
  • Common PTC variants
    • Classic variant: BRAF 40 - 70%, RET / PTC 5 - 40%, RAS 3 - 10%, TERT 10%, NTRK 0 - 5%
    • Follicular variant: RAS 25 - 50%, PAX8 / PPARγ 5 - 30%, BRAF V600E up to 25% (invasive type), TERT 1 -10%, RET / PTC 5%, NTRK 0 - 10%, BRAF K601E < 1%
    • NIFTP: RAS 30 - 45%, PAX8 / PPARγ up to 20%, THADA fusion up to 20%, EIF1AX 5%, absence of BRAF mutation and RET / PTC translocations
    • Microcarcinoma: BRAF 20 - 80%, RET / PTC rearrangements and RAS mutations can be found, TERT < 5%
    • Tall cell variant: BRAF 80 - 100%, TERT 20 - 30%, RET / PTC3
  • Rare PTC variants (based on small series)
    • Columnar variant: BRAF 33%
    • Diffuse sclerosing variant: RET / PTC rearrangement frequently found, while BRAF mutation is uncommon
    • Hobnail variant: BRAF V600E mutation in most cases (50 - 80%), RET / PTC1 is much rarer (up to 20%)
    • Warthin-like variant: BRAF 65%
    • Cribriform-morular variant: RET / PTC rearrangements, RAS mutations and BRAF mutations not identified; germline APC or CTNNB1 mutations in familial adenomatous polyposis coli syndrome
  • Poorly differentiated thyroid carcinoma (PDTC)
    • TERT 30 - 40%
    • RAS 20 - 40%
    • BRAF 5 - 30%, higher rate if arises from PTC
    • EIF1AX 10%
    • Rare chromosomal translocations (RET / PTC, PAX8 / PPARγ, ALK1)
    • Late genetic events are common: TP53 (10 - 40%), CTNNB1 (0 - 25%) and genes that encode effectors of the PI3K-AKT signaling pathway, including PIK3CA, AKT1 and PTEN (10 - 20% collectively)
  • Anaplastic thyroid carcinoma (ATC)
    • Coexisting mutations (median is 6 per case)
    • TP53 50 - 80%
    • TERT 30 - 50%
    • RAS 20 - 50%
    • BRAF 20 - 45%, especially if progress from PTC
    • Less common mutations: CTNNB1 5 - 65%, PIK3CA 5 - 25%, PTEN 5 - 20%, RASAL 15%, EIF1AX 10%
    • Fusions, e.g., ALK, are infrequent
  • Medullary thyroid carcinoma (MTC), sporadic
    • Mutually exclusive RET or RAS mutations
    • RET 30 - 65%, mainly RET M918T
    • RAS 25% (HRAS > KRAS)
  • Medullary thyroid carcinoma (MTC), hereditary
    • Germline RET mutations > 95%, with predominant RET C634A in MEN2A, and RET M918T in MEN2B syndromes, respectively


Clinically significant signatures

Diagnostic molecular signatures
  • Molecular testing is widely used for preoperative triage of patients with thyroid nodules indeterminate on FNA (Bethesda III - V), see Molecular testing in FNA
  • Presence of certain mutations in a sample has high sensitivity and specificity for malignancy, with recommendation for total thyroidectomy instead of diagnostic lobectomy
    • BRAF V600E or RET / PTC rearrangement has virtually 100% risk of malignancy, likely to be conventional or tall cell variant PTC
    • RAS, PAX8 / PPARγ or BRAF K601E confers 75 - 90% risk of cancer, most likely follicular variant PTC
    • TERT, p53 or PIK3CA mutation predicts thyroid cancer (almost 100% risk), particularly advanced disease with propensity for dedifferentiation and distant metastasis
    • RET M918T is associated with MTC (very high accuracy)
  • Single gene testing (usually BRAF V600E) is inexpensive, and can be performed using in house facilities
  • Molecular panels provide the best performance
    • 4 genes (BRAF V600E, RAS, RET / PTC and PAX8 / PPARγ) are essential for any thyroid panel
    • Commercially available panels include early generation (8 and 15 genes) and extended (60+ genes) panels
  • Mutation / fusion panels are highly sensitive for malignancy, often having over 95% positive predictive value ("rule in" cancer), however negative result of mutation test does not always predicts benign thyroid nodule; gene expression classifiers based on mRNA expression signatures provide 95% negative predictive value ("rule out" cancer)
  • Combination of rule in (mutation / fusion panel) and rule out (gene expression classifier) tests is potentially the best approach to indeterminate thyroid nodules, however its cost effectiveness is doubtful

Prognostic significance
  • BRAF V600E is a marker of higher tumor recurrence and tumor related mortality in PTC patients
    • These patients may benefit from more extensive initial surgery with central compartment lymph node dissection to prevent tumor recurrence
    • BRAF mutation is a sensitive, but not a specific marker of tumor aggressiveness
    • Most patients with BRAF V600E mutation do not have recurrent disease and overall survival remains very high in both groups of patients
  • TERT promoter mutations are associated with aggressive phenotype of PTC and FTC, including high persistence / recurrence and increased mortality
    • Recent studies have shown that the prognostic value of TERT mutations is significantly stronger than that of BRAF V600E
  • Combination of BRAF V600E mutation with TERT, AKT1, PIK3CA or TP53 mutations predicts more aggressive tumor behavior
    • Patients with BRAF and TERT mutations alone had recurrence rates of 25% and 50%, respectively, whereas patients with both mutations had a recurrence rate of 70%
Treatment
Therapeutic utility
  • With a high rate of targetable ("druggable") molecular abnormalities in thyroid cancer, genotyping has diagnostic and possibly therapeutic relevance
  • Patients who may benefit from targeted therapy
    • Radioiodine resistant differentiated thyroid cancer (metastatic PTC or FTC)
    • PDTC, ATC
    • MTC
  • The most studied drugs are tyrosine kinase inhibitors (TKI, or MKI, multikinase inhibitors)
    • MKIs block various cell surface (growth factor receptor) and intracellular (members of MAPK signaling) kinases
    • Inhibition of VEGF (vascular endothelial growth factor) mediated pathways contributes to the antiangiogenic effect of MKI
    • Currently, 4 kinase inhibitors are approved for treatment of differentiated thyroid cancer and MTC
      • Sorafenib, an inhibitor of VEGFR1, VEGFR2, VEGFR3, RET (including RET / PTC), RAF (including BRAF V600E), and PDGFRβ (platelet derived growth factor receptor β)
      • Lenvatinib blocks VEGF receptors 1, 2 and 3, FGF receptors 1 - 4, PDGFRα, RET and KIT
      • Vandetanib (VEGFR2, RET, EGFR) and Cabozantinib (VEGFR2, RET, MET) are approved in the USA and EU for treatment of MTC
    • MKI treatment is not curative, and patients eventually develop resistance
  • Other targeted therapies currently in clinical trials:
    • Selective BRAF inhibitors (Vemurafenib, Dabrafenib)
    • PPARγ agonists
    • ALK inhibitors (Crizotinib)
    • Highly selective mTOR inhibitors
    • PTEN modulators
    • NTRK inhibitors
    • Immune checkpoint blockade (anti-CTLA4, anti-PD1, and anti-PDL1)
Microscopic (histologic) images

Images hosted on PathOut server:

Contributed by Andrey Bychkov, M.D., Ph.D.:

V600E mutant protein is diffusely expresed in tumor / cancer, but not normal tissue

Diffuse cytoplasmic staining

Molecular / cytogenetics images

Scroll to see all images.


Images hosted on other servers:

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ALK fusions


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β-catenin (nuclear) in cribriform-morular PTC associated with FAP syndrome


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BRAF V600E (sequencing)

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BRAF V600E (pyrosequencing)

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BRAF V600E (MALDI-TOF)

BRAF V600E / VE1 IHC

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BRAF K601E


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BRAF V600E / VE1

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KRAS mutations

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NRAS mutations (sequencing)

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NRAS Q61R
immunohisto-
chemistry
(melanoma)

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NRAS mutations (pyrosequencing)

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NRAS Q61R
immunohisto-
chemistry
(melanoma)
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PPARγ IHC in FTC (A)

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PTEN IHC (A - C)

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PTEN loss in Cowden syndrome

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PTEN evaluation (breast cancer)


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RET / PTC rearrangements

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RET / PTC rearrangements

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TERT promoter mutations

Videos



Video 1: Molecular influence in thyroid cancer (2014) by The American Head and Neck Society
Video 2: Biomarkers in thyroid cancer - Lessons from TCGA (2015) by Prof. Tom Giordano, University of Michigan
Video 3: Targeted therapies for treatment and management of progressing metastatic thyroid cancer (2015) by Dr. Rebecca Schweppe, University of Colorado Denver
Video 4: Drugs in development for refractory thyroid cancer (2015) by Dr. Daniel Bowles, University of Colorado Denver





Video 5: Molecular targeted therapeutics for medullary thyroid cancer (2015) by Dr. Ann Gramza, NCI