Yuri E. Nikiforov

1
Endocrine Pathology Companion Meeting
Genetic Alterations Involved in the Transition
from Well Differentiated to Poorly Differentiated
and Anaplastic Thyroid Carcinomas

• Yuri E. Nikiforov
• Department of Pathology
• University of Cincinnati

2
Outline

• Genetic events in thyroid WDC, PDC, and AC
• Molecular evidence for progression
• BRAF and RAS mutations
• RET/PTC and PAX8-PPAR?
• rearrangements
• p53 and ß-catenin mutations
• Evidence from LOH studies
• Molecular pathways in progression of thyroid CA
  Summary

3
Molecular Alterations in Thyroid Tumors
Papillary Carcinoma
BRAF RET/PTC RAS
P53 ß-catenin
PDC
AC
RAS
PAX8-PPAR?
Thyroid follicular cell
Follicular Carcinoma
Hurthle Cell Carcinoma
4
BRAF
5
Signaling Pathways Activated by BRAF in Thyroid
Tumors
Y1015
Y1062
SOS
SOS
RAS
Y1096
GRB2
B-RAF
6
Spectrum of BRAF Point Mutations in Various
Tumors
Kinase domain
Val Glu
594
595
598
601
596
599
585
465
465
463
Phe
Gly
Leu
Val
Leu
Gly
Gly
Gly
7
Prevalence of BRAF Mutations in Thyroid Tumors
Nikiforova et al. 2003 Cohen et al., 2003 Xu et
al., 2003 Namba et al., 2003 Fukashima et al.,
2003 Trovisco et al., 2004
8
BRAF Mutations Present in Both Well
Differentiated and Poorly Differentiated
Carcinoma Areas
PDC
PC,WD
DNA
DNA
BRAF
BRAF
Nikiforova et al. (2003)
9
BRAF Mutations in Poorly Differentiated and
Anaplastic Carcinomas
Nikiforova et al. (2003)
10
BRAF Mutations Summary

• PC with BRAF are prone to dedifferentiation and
  transformation to PDC and AC
• Other genetic mutations are required to direct
  this process

Additional mutations
BRAF
PC
11
RAS
12
RAS Mutations

• Point mutations found in many human cancers and
  in most types of thyroid tumors
• K-RAS, H-RAS, N-RAS genes may be involved
• Hot spots - codons 12, 13 and 61
• N-RAS codon 61 mutations most common in thyroid
  tumors

13
Mechanism of RAS Activation by Point Mutation
SOS
GAPs
GDSs
CDC25
Mutations
C3G
codons
12/13 or 61
Downstream
Effectors
14
Molecular Pathways Activated by RAS
Y1062
B-RAF
BAD
Apoptosis
15
Prevalence of RAS Mutations in Thyroid Tumors
16
RAS in Progression of Thyroid Tumors Case
report of AC with areas of FC
AC
Mutations found
RAS codon 61 CAA CGA p53 codon
189 GCC GTC -
Asakawa Kobayashi (2002)
17
Consequences of RAS Activation in Thyroid Cells

• Development of nodules, adenomas, and carcinomas
  in transgenic mice
• Increased cell proliferation but insufficient for
  complete transformation of cultured cells
• Increased chromosome instability, i.e.
  micronuclei, centrosome amplification, chromosome
  misalignment during mitosis

18
RAS Mutations Summary

• Predispose FC and PC to dedifferentiation, likely
  by increasing genomic instability
• Require additional mutations for
  dedifferentiation

Additional mutations
PC
RAS
19
RET/PTC Rearrangement
20
RET/PTC Rearrangements
21
Molecular Pathways Activated by RET/PTC
RET/PTC
Y1015
SOS
GRB2
Y1062
22
Prevalence of RET/PTC in Thyroid Tumors
23
RET/PTC Rearrangements Summary

• No RET/PTC in anaplastic carcinomas
• Data on PDC not entirely conclusive
• Likely - PC with RET/PTC have low potential for
  dedifferentiation/progression

RET/PTC
PC
24
Molecular Pathways in Thyroid Papillary
Carcinogenesis
BRAF
PC
40
RAS
PC
15
RET-PTC
PC
20
25
PAX8-PPAR? Rearrangement
26
Structure of PAX8-PPAR? Fusion Protein
Kroll et al. (2000)
27
PAX8-PPAR? Rearrangement

• Results from fusion of PAX8 (2q13) and PPAR?
  (3p25) genes
• PAX8-PPAR? chimeric protein has dominant negative
  effect on wild-type PPAR?
• Wild-type PPAR? may inhibit thyroid cell growth
  (tumor suppressor gene)

28
Prevalence of PAX8-PPAR? in Thyroid Tumors
29
PAX8-PPAR? Rearrangements Summary

• No RET/PTC in PDC and AC
• Likely - FC with PAX8-PPAR? lack potential for
  dedifferentiation/
• progression

PAX8-PPAR?
30
Molecular Pathways in Thyroid Follicular
Carcinogenesis
FC
FA
RAS
45
PAX8-PPAR?
35
31
Mutations Directing Progression/
Dedifferentiation of Thyroid Tumors p53
32
Mutations Directing Progression/
Dedifferentiation of Thyroid Tumors ß-catenin
33
Specific Genetic Events in Thyroid Tumors
Summary
34
Molecular Evidence for Progression/Dedifferentiati
on LOH Studies

• In the same tumor, WDC and AC components have
  similar patterns of allelic loss
• Increased LOH rate in AC component

J. Hunt et al. (2003)
35
Molecular Pathways in Progression of Thyroid
Carcinomas Summary

• Studies of gene mutations and LOH supports the
  following progression
• WDC PDC AC
• WD tumors with BRAF and RAS mutations are prone
  for dedifferntiation, but require additional
  mutations
• p53 and possibly ß-catenin directly guide
  progression

36
Acknowledgements
James Fagin University of Cincinnati Todd Kroll
Emory University Giovanni Tallini

• Nikiforov Lab
• Marina Nikiforova
• Zhaowen Zhu
• Raffaele Ciampi
• Christy Caudill
• Manoj Gandhi