1. MOLECULAR BASIS OF THYROID NEOPLASM
Speaker- Dr Subhasish Saha
Moderator- Dr Manisha Mahata
Department of Pathology
R G Kar Medical College & Hospital
2. INTRODUCTION
Thyroid cancer is most common endocrine malignancy, incidence
growing steadily( 0.5-10 cases per 100,000 populations).
Women are 3 times more common than male.
Benign thyroid neoplasm outnumbers malignancy by a ratio of
10:1.
More than 95% of thyroid cancers - thyroid follicular cells.
2-3% of thyroid tumors (medullary thyroid cancers) - C-cells.
Radiation exposure, iodine deficiency are few of the risk factors
5. CONTD…
Papillary carcinoma (approximately 80%).
follicular carcinoma (approximately 15%).
Poorly differentiated and anaplastic thyroid carcinomas can
arise de novo or from the preexisting well differentiated
papillary or follicular carcinoma.
Medullary thyroid carcinoma- 3% of all thyroid cancers.
6. Rapidly expanding knowledge of molecular genetics of thyroid
cancer has started to translate into clinical practice, offering
significant improvement in accuracy of the preoperative diagnosis
of thyroid cancer and better tumor prognostication.
CONTD…
8. AVERAGE PREVALENCE OF MUTATIONS IN VARIOUS
TYPES OF THYROID CANCER
Tumor Type Prevalence
Papillary carcinoma
BRAF 40-45%
RET/PTC 10-12%
RAS 10-12%
TRK <5%
Follicular Carcinoma
RAS 40-50%
PAX8/PPAR 30-35%
PIK3CA <10%
PTEN <10%
11. THYROID ADENOMA
Benign neoplasm derived from follicular epithelium.
Usually solitary.
Majority of adenomas are nonfunctional, a small proportion
produces thyroid hormones ("toxic adenomas") and cause
clinically apparent thyrotoxicosis.
Follicular adenoma shared genetic alterations support – possibility
that at least of subset of follicular carcinoma arise in preexisting
follicular adenoma.
12. PATHOGENESIS OF FOLLICULAR ADENOMA
Thyroid adenoma have mutation of RAS or PIK3CA or bear a
PAX8-PPAR fusion gene- genetic alteration are similar to those
seen in follicular carcinoma.
13. PAPILLARY CARCINOMA
Papillary carcinoma carries point mutations of BRAF ,RAS gene ,
RET/PTC and TRK rearrangements.
They are able to activate mitogen-activated protein kinase
(MAPK) pathway .
These mutually exclusive mutations are found in >70% of
papillary thyroid carcinomas.
14. PATHOGENESIS OF PAPILLARY THYROID
CARCINOMA
MAPK pathway
and its activating
genetic alterations
in PTC
15. CONTD.....
MAPK pathway serves to propagate signals from cell membrane
receptor tyrosine kinase (RTK) to the nucleus through a series of
adaptor proteins and intracytoplasmic kinase including RAS,RAF
(mainly BRAF in thyroid follicular cells), MEK, and ERK.
Activated ERK translocates to the nucleus and regulates
transcription of genes involved in cell differentiation, proliferation,
and survival.
In thyroid cancer, activation of this pathway occurs owing to point
mutations of RAS and BRAF or as a result of RET/PTC and TRK
rearrangements involving the RET and NTRK1 genes,
respectively.
16. FOLLICULAR CARCINOMA
Follicular carcinomas -harbor either RAS mutations or
PAX8/PPAR rearrangement.
These mutations are also mutually exclusive , identified in 70% to
75% of cases.
Genetic alterations involving the PI3K/AKT signaling pathway
occur in thyroid tumors, rare in well-differentiated thyroid cancer
and have higher prevalence in less differentiated thyroid
carcinomas.
20. RAF MUTATION
Three types of RAF kinase- A RAF, B RAF, C RAF.
Most mutations seen in thyroid cancer are point mutations
that involve nucleotide 1799 and result in a valine-to glutamate
substitution at residue 600 (BRAFV600E).
Mutation in other codon identified- codon 598, 599,601.
BRAF V600E mutation most commonly - conventional PTC , tall
cell variant of PTC & least commonly - follicular variant of PTC,
BRAF mutation – anaplastic & poorly differentiated carcinoma.
21. CONTD....
Point mutations of the BRAF gene are the most common
genetic alteration known to occur in thyroid papillary
carcinomas (40% to 45%)-mutation leads to constitutive
activation of BRAF kinase and chronic stimulation of the MAPK
pathway, tumorigenic for thyroid cells.
In 1% to 2% of papillary carcinomas, other BRAF mutations can
be found, including K601E point mutation and small in-frame
insertions or deletions surrounding codon 600, as well as
AKAP9/BRAF rearrangement which is more common in papillary
carcinomas associated with radiation exposure.
22.
23. SIGNIFICANCE OF BRAF MUTATION
BRAF V600E has not been found in follicular carcinomas ,benign
thyroid nodules.
Specific marker of papillary carcinoma and related tumor types.
Got diagnostic & prognostic significance.
Molecular testing for BRAF V600E in thyroid fine-needle
aspiration (FNA) samples significantly improves the accuracy of
cytologic diagnosis of thyroid nodules-helps in establishing
definitive diagnosis of cancer in nodules with indeterminate
cytology.
24. Prognostic marker for papillary thyroid carcinoma. Associated
with aggressive tumor - extrathyroidal extension, advanced tumor
stage at presentation, lymph node or distant metastases.
Independent predictor of- treatment failure and tumor recurrence,
even in patients with low-stage disease an in-dependent risk for
tumor-related death.
SIGNIFICANCE OF BRAF MUTATION
25. BRAF mutation would be of particular importance in T1 papillary
carcinomas(tumors 2 cm or less in size) and papillary
microcarcinomas ( incidentally discovered tumors measuring 1 cm
or less).
Both these categories has been strongly associated- with
extrathyroidal extension and lymph node metastases.
SIGNIFICANCE OF BRAF MUTATION
26. It is important to note that the association with tumor
aggressiveness is limited to the BRAF V600E mutation and is not
found other rare types of BRAF mutation.
Patients with BRAF V600E–positive nodules, detected
preoperatively in FNA samples, would benefit from more extensive
initial surgery and from postsurgical radioiodine treatment with
higher dose, and require close follow-up of patient.
SIGNIFICANCE OF BRAF MUTATION
27. patients with BRAF V600E–positive nodules, detected
preoperatively in FNA samples, would benefit from more
extensive initial surgery and from postsurgical
radioiodine treatment with higher dose, and require
close follow-up of patient.
SIGNIFICANCE OF BRAF MUTATION
28. RET/PTC REARRANGEMENTS
RET proto-oncogene encodes a cell membrane receptor tyrosine
kinase. RET is highly expressed in thyroid parafollicular or C cells
but not in follicular cells.
It is activated by chromosomal rearrangement known as
RET/PTC rearrangement.
In RET/PTC, the portion of RET coding for the tyrosine kinase
domain is fused to various unrelated genes.
11 types of RET/PTC rearrangements have been reported- formed
by RET fusion to different genetic partners.
29. 2 most common rearrangement types-RET/PTC1 and RET/PTC3,
account for most rearrangements found in thyroid cancer.
All fusions contain the intact tyrosine kinase domain of the RET
receptor, which enables the RET/PTC protein to activate the
MAPK signaling pathway
RET/PTC REARRANGEMENTS
30. SIGNIFICANCE OF RET/PTC REARRANGEMENT
Clonal RET/ PTC - reasonably specific for papillary thyroid carcinoma.
Clonal RET/PTC rearrangements are found in 10% -20% of adult
sporadic papillary carcinomas.
RET/PTC rearrangements occur with higher incidence in patients
with a history of radiation exposure (50%–80%) and in children and
young adults(40%–70%).
RET/PTC1 is typically the most common rearrangement type and
comprises up to 60% to 70% of all positive cases.
RET/PTC3 accounts for 20% to 30% cases.
RET/PTC2 and other novel rearrangement types are< 5% of all positive
cases.
31. Papillary carcinomas with RET/PTC rearrangements
typically present at younger age and have classic
papillary histology and a high rate of lymph node
metastases.
SIGNIFICANCE OF RET/PTC REARRANGEMENT
32. Correlation of RET/PTC rearrangement & prognosis of papillary
carcinomas remains unclear.
In some study RET/PTC rearrangement is associated with more
favorable behavior, &very low probability of progression to poorly
differentiated and anaplastic carcinomas.
Some study shows- tumors carrying RET/PTC3 rearrangement
may be prone to dedifferentiation and more aggressive behavior.
SIGNIFICANCE OF RET/PTC REARRANGEMENT
33. Testing for RET/PTC rearrangements helpful for - diagnosis of
thyroid cancer.
Detection of clonal RET/PTC is a strong indicator of papillary
carcinoma.
In thyroid FNA samples, RET/PTC detection can improve the
preoperative diagnosis of thyroid nodules, particularly in samples
that are indeterminate by cytology or have an insufficient amount
of cells for cytologic evaluation.
SIGNIFICANCE OF RET/PTC REARRANGEMENT
34. RAS
3 type of RAS genes - HRAS, KRAS, and NRAS genes.
They encode highly related G proteins that are located at the inner
surface of the cell membrane and propagate signals arising from
cell membrane receptor tyrosine kinase and G-protein–coupled
receptors along the MAPK, PI3K/AKT, and other signaling
pathways.
Activating point mutations in the discrete domains of the RAS
genes (codons 12/13 and 61) are common in different types of
human tumors.
Thyroid tumors the most frequent mutations involve NRAS codon
61 and HRAS codon 61. (other cancer KRAS codon 12/13
mutations predominate)
35. CONTD….
RAS mutations are found with variable frequency in all types of
thyroid follicular cell-derived tumors.
In papillary thyroid carcinomas, RAS mutations occur in 10% to
20% of tumors( Follicular variant of papillary carcinoma )
RAS mutations are also found in 40% to 50% of conventional-type
follicular carcinomas and 20% to 40% of conventional-type
follicular adenomas.
36. SIGNIFICANCE OF RAS
RAS mutations in thyroid carcinomas correlate with tumor
dedifferentiation and less favorable prognosis.
Strong correlation between RAS mutation and metastatic behavior
of follicular and papillary carcinomas, especially with respect to
bone metastases has been found.
Detection of RAS mutation in a thyroid nodule provides
strong evidence for neoplasia, although it does not establish the
diagnosis of malignancy.
37. The importance of RAS mutation detection - it represents a
marker of the follicular variant of papillary carcinoma, which is
most difficult to diagnose, especially by FNA cytology.
RAS mutation apparently predisposes the well-differentiated
cancer to dedifferentiation and more aggressive behavior.
Therefore, surgical removal of follicular adenomas that carry this
oncogenic mutation is justified to prevent progression.
SIGNIFICANCE OF RAS
38.
39. PAX8/PPAR
PAX8/PPAR rearrangement is a result of t(2;3)(q13;p25)
translocation that leads to the fusion between the PAX8 gene,
which encodes a paired domain transcription factor and the
peroxisome proliferator–activated receptor (PPAR) gene.
PAX8/PPAR is found in 30% to 40% of conventional-type
follicular carcinomas and with lower prevalence in oncocytic
carcinomas.
This rearrangement is also found in the follicular variant of
papillary carcinoma, (5-38%) follicular adenomas(2-13%)
40. Tumors harboring PAX8/PPAR tend to present-
Younger age.
Smaller in size.
Vascular invasion.
PAX8/PPAR rearrangements and RAS point mutations rarely
overlap in the same tumor suggesting that follicular carcinomas
may develop via at least 2 distinct molecular pathways- either
PAX8/PPAR or RAS mutation.
SIGNIFICANCE OF PAX8/PPAR
41. Detection of PAX8/PPAR rearrangement in a follicular lesion is
not fully diagnostic for malignancy by itself, but it should prompt
the pathologist to perform an exhaustive search for vascular or
capsular invasion.
PAX8/PPAR rearrangement can be detected in thyroid FNA
samples, and this typically correlates with the presence of
malignancy.
SIGNIFICANCE OF PAX8/PPAR
42. OTHER GENETIC ALTERATIONS
Rare types of somatic mutations found in thyroid papillary
carcinoma include TRK rearrangement. It is found in < 5% of
papillary carcinoma.
At least 3 types of the rearrangement exist, formed by fusion of the
NTRK1 gene to different partners. The diagnostic utility of testing
for TRK rearrangement is limited.
43. Expression of various microRNAs (miRNAs) appears to differ
between papillary carcinomas and benign thyroid lesions .
Used diagnostically in thyroid surgical and FNA samples.
Several miRNAs, including miR-146b, miR-221, miR-222, miR-
181b, miR- 155, and miR-224, have been found to be significantly
upregulated in papillary carcinomas .
Several upregulated miRNAs have been reported in thyroid
follicular carcinoma.
OTHER GENETIC ALTERATIONS
44. GENETIC ALTERATION IN FOLLICULAR CELL DERIVED
MALIGNACIES OF THYROID
Papillary
carcinoma
(Translocation
/inversion)
RAS
GTP
BRAFPapillary
carcinoma(poi
nt mutation)
MEK
ERK
PI3K
FCT&
Anaplastic
CA ( Point
mutation)
PDK1
PTEN
AKT
PAX8/PPAR
Cell growth,
proliferation,differ
entiation
Follicular
carcinoma(Tra
nslocation)
RET/PTC
45. SUMMARY
Many genetic mutations and other molecular alterations occurring
in thyroid carcinomas has been discovered .
These alterations, particularly specific mutations, can be reliably
detected by molecular techniques in thyroid can be used
successfully to improve cancer diagnosis and management of
patients with thyroid nodules.
Diagnostic use of BRAF mutation, which is highly specific for
malignancy when detected using well-validated techniques has
been established.
46. Biggest diagnostic impact can be achieved by testing FNA samples
for a panel of mutations that typically includes BRAF, RAS,
RET/PTC, and PAX8/PPAR.
Finding any of these mutations in a thyroid nodule provides strong
indication for malignancy and helps to refine clinical management
for a significant proportion of patients with indeterminate
cytology.
The use of these and other emerging molecular markers is
expected to improve significantly the accuracy of cancer diagnosis
in thyroid nodules and allow more individualized surgical and
postsurgical management of patients with thyroid cancer.
SUMMARY
47. REFERENCES….
Rosai & Ackerman’s Surgical Pathology- 10th edition , Volume1.
Christopher D.M. Fletcher Diagnostic histopathology of tumors- 3rd
edition, volume 2.
Robbins & Cotran Pathological basis of Diseases – 8th edition.
Mingzhao Xing-BRAF Mutation in Papillary Thyroid Cancer:
Pathogenic Role, Molecular Bases, and Clinical Implications
Division of Endocrinology and Metabolism, the Johns Hopkins
University School of Medicine .28(7):742–762
JAMES A. FAGIN-Genetics of papillary thyroid cancer
initiation:Implications for therapy. The American Clinical and
Climatological Association, Vol. 116, 2005.
