Transcript Familial breast cancer

Familial Cancer Syndromes
• the familial occurrence of cancer
• clinical oncogenetics
• hereditary breast- en ovarian cancer
• hereditary colorectal cancer
Causes of cancer
Causes of cancer:
environmental
hereditary
Hereditary factors: evidence
positive family history
twin studies
occurrence cancer in certain ethnic groups
History for breast cancer
Factor
Relative risk
High risk group
Age
>10
elderly
Ethnicity
5
Western society
Age at menarche
3
<11 years of age
Age at menopauze
2
>54 years of age
Age at first full term
pregnancy
Family history
3
>40 years of age
>2
Bening breast disease
4-5
1st degree relative, young age
at diagnosis
Atypical hyperplasia
Carcinoma in the other
breast
Socio-economical group
4
2
Lower socio-economical group
Diet
1.5
High intake of saturated fat
The familial occurrence of cancer
8
Relative risk
3
population
risk
1
Cumulative risk
~12%
sporadic
~80%
to 30%
familial
15%
Contribution of environmental factors
Contribution of genetic factors
to 90%
hereditary
5%
Determinants
General
• ‘closeness’ of relatives
• age at diagnosis
• ratio affected to ‘at risk’
Breast cancer:
• 1 or > first degree relatives
• young age (<50 years)
• bilateral breast cancer or ovarian cancer
• breast cancer in males
Hereditary vs. familial: breast cancer
hereditary breast- and ovarian cancer
familial breast cancer
OvCa 40j
BrCa 50j
BrCa 38j
Bil BrCa 41&47j
BrCa 39j
A priori risk: highly increased
BrCa 53j
A priori risk: moderately increased
Genetic contribution to cancer
General:
twin studies: concordant vs. discordant
contribution: limited
important in:
colorectal cancer
breast cancer
prostate cancer
Family cancer syndromes
Definition:
Clinical syndrome characterized by the preferential
occurrence of certain tumors in a family
often: specific tumors
sometimes: associated clinical signs
Inheritance
All family cancer syndromes: segregation and
therefore monogenic
all known: autosomal inheritance
most: dominant
some: recessive
most: genetic heterogeneity
variable penetrance
Autosomal dominant inheritance
+/+
-/+
-/+ : carrier
-/+
-/+
+/+
+/+
-/+
1 of the parents: affected
risk: 50%
independent of gender
affected relatives in all generations
+/+ : wild type
+/+
Autosomal recessive inheritance
+/+
-/+
-/+
-/- : affected
-/+
-/+ : carrier, unaffected
+/+ : wild type
+/+
-/+
generally no affected parents
risk: 25%
independent of gender
no affected relatives
-/+
-/-
The Knudson hypothesis
family cancer syndromes
hyperplasia
metaplasia dysplasia
Additional genetic aberrations
Sporadic tumors
CIS
Knudson and dominant inheritance
-
+
-
gametogenesis
+
gametogenesis
-
+
-
Family cancer syndromes
Autosomal dominant
Adenomatous polyposis
Hereditary Non-Polyposis Colorectal Cancer (HNPCC)
Hereditary Breast- and Ovarian Cancer (HBOC)
Li-Fraumeni
Neurofibromatosis
Retinoblastoma
Von Hippel Lindau
VHL
Wilms’ tumors
Autosomal recessive
Ataxia teleangiectasia
Bloom syndrome
Werner’s syndrome
Fanconi’s anemia
Xeroderma pigmentosum
APC
MLH1, MSH2, MSH6
BRCA1, BRCA2
TP53, CHK2
NF1, NF2
RB
WT1, 2 & 3
ATM
BLM
WRN
FACC
XPA-E, ERCC2-5
Tumor suppressor genes
Gatekeepers:
direct inhibitors van cell growth
e.g.: APC
Landscapers:
modulate the micro-environment
e.g.: NF1
Caretakers:
DNA repair genes
e.g.: mismatch repair genes MLH1, MSH2, MSH6
Clues to an inherited predisposition to cancer
young age at diagnosis
aggregation of rare tumors
association with congenital malformations
multiple primary tumors in an individual
bilateral tumors in paired organs
positive family history
tumor types
inheritance pattern
clinical aberrations
clinical diagnosis
indication for molecular
genetic testing
genetic counseling
follow-up
risk in unaffected relatives
Genetic counseling
1st counseling: intake
mutation analysis
no indication for mutation analysis
2nd counseling:communication of test results
no mutation
empirical risk estimation
BRCA1 or BRCA2 mutation
follow-up & preventive measures
presymptomatic testing
Informed consent
Issues:
•
•
•
•
•
•
•
•
•
•
•
•
•
the right not to be tested
purpose of genetic testing
reliability of genetic testing
course of genetic testing
cost of genetic testing
implications of both positive and negative test results
the possibility that no additional risk information will be obtained
at the completion of the test
the options for approximation of risk without genetic testing
disadvantages of genetic testing
confidentiality of the test results
possibility of discrimination
preventive measures - limited proof of efficacy
risk for carriership in children
Mutation analysis
Techniques:
• PTT (protein truncation test)
• DGGE (denaturing gradient gel electrophoresis)
• Southern blot
• PCR cDNA and gDNA
• direct sequencing
Detetection ratio:
• dependent of mutational spectrum
• dependent of the used techniques
• dependent of the a priori chance of finding a mutation
in a family member
Molecular genetics testing: PTT
Forward primer
GGATCC TAATACGACTCATATA GGAACAGAC CAGCATGG
Bacteriophage T7 promotor translation initiation
signal
PCR
T7
in vitro transcription/
translation
T7 polymerase
lysate
Rnase inhibitor
amino acids without leucine
H³ leucine
AUG
RNA
peptide
Technique of choice
for the detection of
nonsense
mutations e.g.:
BRCA1&2 exon 11
SDS - PAGE
autoradiography
normal length
(62 kDa)
normal length
(51 kDa)
truncated peptide (30 kDa)
truncated peptide (22 kDa)
Molecular genetic testing: DGGE
Wild type DNA ( allel A)
GC-clamp
Mutant DNA ( allel B)
G
A
GC-clamp
C
T
analogous to:
SSCP
Heteroduplex analysis
denaturation
G
A
C
T
re-annealing
homoduplex DNA
heteroduplex DNA
G
allele AA
allele BB
G
C
allele AB
T
C
A
T
allele BA
A
AA
BB
AB
low concentration UF
HETERODUPLEXES
HOMODUPLEXES
high concentration UF
technique of choice for:
• substitutions
• small deletions and
insertions
Presymptomatic testing
Definition
genetic testing for a known mutation in an unaffected ‘at
risk’ relative
-
+
+
BRCA1 Q1281X
+
+
+
+
+
+
+
-
Hereditary breast- and ovarian cancer
Clinical description:
Breast and/or ovarian cancer:
• in at least 3 first degree relatives or
3 second degree relatives (in case
of paternal transmission)
• in at least two successive generations
• in at least one patient: Dx <50 years of age
Inheritance: autosomal dominant
Genes:
• BRCA1 & BRCA2 (~80%)
Epidemiology
85%
sporadic
familial and hereditary
15%
~40%
monogenic
familial
~60%
Molecular genetics
BRCA1
BRCA2
both genes: ~800 different mutations
no ‘hotspots’, strong ‘founder effects’
mutations: spread over coding sequence
as well as in non coding parts
wide array of different types
Founder mutation
Mutation that is particularly frequent in a certain
population due to a common ancestor
characteristic:
markers surrounding the mutation are in‘linkage
disequilibrium’
Linkage disequilibrium:
A condition where two genes are found together in a
population at a greater frequency than that predicted
simply by the product of their individual gene
frequencies.
Founder mutation
‘old’
‘recent’
Founder mutation
BRCA1 IVS5+3A>G
Consensus splice donor sequence
C
A
AG GT AGT
A exon intronG
Wild type BRCA1 exon 5 splice donor
AAG GTATAT
‘Consensus value’
0,92
exon 5 intron 5
BRCA1 IVS5+3A>G exon 5 splice donor
TATGTAAGA---- AAG GTGTAT
0,53
22
0,91
Founder mutation BRCA1 IVS5+3A>G
DGGE
Exon 5
Sequencing
Intron 5
BRCA1 & BRCA2: molecular profiling
Follow-up
Counseling
• non-directive
• conjointly with referring physician
Interventions
• intensive screening
• prophylactic surgery
• chemoprophylaxis
Evidence
• limited proof of efficacy
• few prospective studies
Example
-
+
BrCa 53j
phenocopy
BRCA1 Q1281X
+
+
Bil. BrCa 36&46j
+
+
BrCa 29j
+
+
BrCa 51j
+
+
-
Familial breast cancer: conclusions
Hereditary breast- and ovarian cancer:
• Major contribution of BRCA1 & BRCA2
• Genetic testing: useful
• Small group of patients with highly increased risk
Familial breast cancer:
• Minor contribution of BRCA1 & BRCA2
• Genetic testing: limited use
• Large group of patients with moderately increased risk
• Probably: genetic variants, ‘modifier genes’, multifactorial
inheritance
Familial prediposition to colorectal cancer
Hereditary colorectal cancer
HNPCC: hereditary non-polyposis colorectal carcinoma
FAP: familial adenomatous polyposis
Familial colorectal cancer
Preferential occurrence of colorectal cancer in a family
without evidence for a heritable cancer syndrome
Familial Polyposis Adenomatous
Definition:
familial colorectal cancer syndrome characterized by the
predisposition to develop 100 to 1000 polyps
Familial Adenomatous Polyposis
Molecular Genetic Testing
FAP:
autosomal dominant inheritance
mutations in the APC gene
complete coding sequence
mutation analysis
~90% mutations: nonsense mutations
PTT on cDNA
APC mutations in ~80% of the FAP families
Adenoma/carcinoma sequence
APC: genotype/phenotype correlations
3’
5’
NH2
COOH
CHRPE +
Classical FAP
Attenuated FAP
Desmoïd tumors 10-20 %
Attenuated FAP
Desmoïd tumors ca. 100%
Hereditary desmoid disease
Follow-up
As soon as polyps are detected:
prophylactic colectomy
HNPCC
Definition:
familial cancer syndrome characterized by a highly
increased risk for colorectal (~80%) and endometrial
cancer (~60%)
Clinical description (Amsterdam I criteria):
Colorectal cancer:
• in at least 3 relatives, one of which is a first degree
relative of the other two
• age at diagnosis in at least one patient <50 years
• in at least two successive generations
• FAP is excluded
Molecular genetics
genes:
• hMLH1
• hMSH2
• hMSH6
complete coding sequence
mutation-analyse :
• DGGE
• Southern Blot
Additionally MSI en immunohistochemistry
Microsatellite instability
Mismatch repair
Microsatellites
Short stretches of repititive
sequences
mono-, di- and trinucleotide
repeats
‘slippage’ of DNA polymerase
Microsatellite instability
Tumor:
defective mismatch
repair
Other tissues:
normal mismatch
repair
Microsatellite instability
instability microsatellite
D2S123
instability microsatellite
BAT25
B
B
T
T
Microsatellite instability
Microsatellite instability
High MSI:
prognostically favorable,
even in sporadic colorectal
carcinomas
Immunohistochemistry
2 hit model: absent expression of the mutant tumor
suppressor in the tumor
normal
MSI-H
MSS
Tumor characteristics
 predeliction for the proximal colon;
 undifferentiated growth pattern (solid or cribriform)
 strong lymphocyte aggregation around the tumor
colon transversum
colon ascendens
colon descendens
MIN en CIN: gatekeepers and caretakers
MIN: microsatellite instability
• mutation in caretakers
• euploid
• proximal colon (colon ascendens)
• slow initiation, fast progression
CIN: chromosomal instability
• mutation in gatekeeper
• aneuploid
• distal
• fast initiation, slow progression
(NER: nucleotide excision repair)
Conclusions
Family cancer syndromes: small group of patients with a highly
increased risk, monogenic inheritance
Familial tumors: large group of patients, moderately increased risk,
probably multifactorial inheritance, considerable contribution of
environmental factors
Genetic testing: especially useful in family cancer syndromes
Hereditary vs. familial: clinical distinction
Combination of different mutation analysis techniques: optimization of
the mutation detection rate
Mutation analysis: laborious and time consuming
Study of familial cancer syndromes: insights into biological processes
essential in the etiology and the progression of cancer and vice versa