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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 - PowerPoint PPT Presentation
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Familial Cancer Syndromes
• the familial occurrence of cancer
• clinical oncogenetics
• hereditary breast- en ovarian cancer
• hereditary colorectal cancer
Causes of cancer
Causes of cancer:environmentalhereditary
Hereditary factors: evidencepositive family historytwin studiesoccurrence 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 termpregnancy
3 >40 years of age
Family history >2 1st degree relative, young ageat diagnosis
Bening breast disease 4-5 Atypical hyperplasia
Carcinoma in the otherbreast
4
Socio-economical group 2 Lower socio-economical group
Diet 1.5 High intake of saturated fat
The familial occurrence of cancer
hereditary5%
familial15%
Contribution of genetic factors
sporadic~80%
Cumulative risk
Contribution of environmental factors
populationrisk
8
3
1
Relative risk
~12% to 30% to 90%
Determinants
Breast cancer:• 1 or > first degree relatives• young age (<50 years)• bilateral breast cancer or ovarian cancer• breast cancer in males
General• ‘closeness’ of relatives• age at diagnosis• ratio affected to ‘at risk’
OvCa 40j
BrCa 38j
BrCa 39j
BrCa 50j
BrCa 53j
A priori risk: moderately increased
A priori risk: highly increased
familial breast cancerhereditary breast- and ovarian cancer
Hereditary vs. familial: breast cancer
Bil BrCa 41&47j
Genetic contribution to cancer
General:twin studies: concordant vs. discordantcontribution: limitedimportant in:
colorectal cancerbreast cancerprostate cancer
Family cancer syndromes
Definition:Clinical syndrome characterized by the preferential occurrence of certain tumors in a family
often: specific tumorssometimes: associated clinical signs
Inheritance
All family cancer syndromes: segregation and therefore monogenic
all known: autosomal inheritance
most: dominantsome: recessive
most: genetic heterogeneityvariable penetrance
Autosomal dominant inheritance
1 of the parents: affectedrisk: 50%independent of genderaffected relatives in all generations
-/++/+
-/+
-/+ -/+
+/+
+/+ +/+
-/+ : carrier
+/+ : wild type
Autosomal recessive inheritance
generally no affected parentsrisk: 25%independent of genderno affected relatives
-/+ : carrier, unaffected
+/+ : wild type
-/- : affected-/++/+
-/+
+/+ -/+
-/+
-/+ -/-
The Knudson hypothesis
family cancer syndromes
Sporadic tumorsAdditional genetic aberrations
hyperplasia metaplasia dysplasia CIS
Knudson and dominant inheritance
+ -
gametogenesis
-
gametogenesis
- -+ +
Family cancer syndromes
Autosomal dominantAdenomatous polyposis APCHereditary Non-Polyposis Colorectal Cancer (HNPCC) MLH1, MSH2, MSH6Hereditary Breast- and Ovarian Cancer (HBOC) BRCA1, BRCA2Li-Fraumeni TP53, CHK2Neurofibromatosis NF1, NF2Retinoblastoma RBVon Hippel Lindau VHLWilms’ tumors WT1, 2 & 3
Autosomal recessiveAtaxia teleangiectasia ATMBloom syndrome BLMWerner’s syndrome WRNFanconi’s anemia FACCXeroderma pigmentosum XPA-E, ERCC2-5
Tumor suppressor genes
Gatekeepers:direct inhibitors van cell growthe.g.: APC
Landscapers:modulate the micro-environmente.g.: NF1
Caretakers:DNA repair genese.g.: mismatch repair genes MLH1, MSH2, MSH6
Clues to an inherited predisposition to cancer
clinical diagnosis
indication for molecular genetic
testing
genetic counselingfollow-up
risk in unaffected relatives
young age at diagnosisaggregation of rare tumorsassociation with congenital
malformationsmultiple primary tumors in an
individualbilateral tumors in paired organs
positive family historytumor typesinheritance
patternclinical
aberrations
Genetic counseling
1st counseling: intake
empirical risk estimation follow-up & preventive measures presymptomatic testing
BRCA1 or BRCA2 mutationno mutation
2nd counseling:communication of test results
mutation analysis
no indication for mutation analysis
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 primerGGATCC TAATACGACTCATATA GGAACAGAC CAGCATGG
Bacteriophage T7 promotortranslation initiation signal
T7
PCR
in vitro transcription/ translation
SDS - PAGE autoradiography
AUGRNA
peptide
normal length (51 kDa)
truncated peptide (30 kDa)
normal length(62 kDa)
truncated peptide (22 kDa)
T7 polymeraselysateRnase inhibitoramino acids without leucineH³ leucine
Technique of choice for the detection of nonsense mutations e.g.: BRCA1&2 exon 11
Molecular genetic testing: DGGE
GC-clamp GC-clamp
Wild type DNA (allel A) Mutant DNA (allel B)
G
C
A
T
denaturation
G
C
A
T
re-annealing
GC
AT
homoduplex DNA
allele AA
allele BB
heteroduplex DNA
G
TC
A
allele AB
allele BA
AA BB AB
HETERODUPLEXES
HOMODUPLEXES
low concentration UF
high concentration UF
technique of choice for:• substitutions• small deletions and
insertions
analogous to:SSCPHeteroduplex analysis
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 least3 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
sporadicfamilial and hereditary
15%
85%
monogenicfamilial~40%
~60%
Molecular genetics
BRCA2 BRCA1
both genes: ~800 different mutationsno ‘hotspots’, strong ‘founder effects’mutations: spread over coding sequence as well as in non coding parts
wide array of different types
Founder mutation
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.
Mutation that is particularly frequent in a certain population due to a common ancestor
characteristic:markers surrounding the mutation are in‘linkage disequilibrium’
Founder mutation
‘old’ ‘recent’
Founder mutation
BRCA1 IVS5+3A>G
‘Consensus value’
0,92
Wild type BRCA1 exon 5 splice donor
GTATATAAGexon 5 intron 5
Consensus splice donor sequence
GT AGTAG
AGCA
intronexon
0,53
BRCA1 IVS5+3A>G exon 5 splice donor
GTGTATAAG TATGTAAGA----
0,9122
Founder mutation BRCA1 IVS5+3A>G
Sequencing
Intron 5Exon 5
DGGE
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
+
+
+
+++
+
-
-
+
Bil. BrCa 36&46j
BrCa 29j
BrCa 51jBrCa 53j
BRCA1 Q1281X
+
phenocopy
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
Familial colorectal cancerPreferential occurrence of colorectal cancer in a family without evidence for a heritable cancer syndrome
Hereditary colorectal cancerHNPCC: hereditary non-polyposis colorectal carcinomaFAP: familial adenomatous polyposis
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 inheritancemutations in the APC gene
complete coding sequence
mutation analysis~90% mutations: nonsense mutationsPTT on cDNAAPC mutations in ~80% of the FAP families
Adenoma/carcinoma sequence
APC: genotype/phenotype correlations
Desmoïd tumors 10-20 % Desmoïd tumors ca. 100% Hereditary desmoid disease
CHRPE +
Attenuated FAP
Classical FAP
Attenuated FAP
NH2 COOH
3’5’
Follow-up
As soon as polyps are detected: prophylactic colectomy
HNPCC
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
Definition:familial cancer syndrome characterized by a highly increased risk for colorectal (~80%) and endometrial cancer (~60%)
Molecular genetics
genes: • hMLH1• hMSH2• hMSH6
complete coding sequence
mutation-analyse : • DGGE• Southern Blot
Additionally MSI en immunohistochemistry
Microsatellite instability
MicrosatellitesMismatch repair
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 microsatelliteD2S123
instability microsatelliteBAT25
B
T
B
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
MSSnormal MSI-H
Tumor characteristics
predeliction for the proximal colon; undifferentiated growth pattern (solid or cribriform) strong lymphocyte aggregation around the tumor
colon ascendens
colon transversum
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