Transcript Genetics of Colorectal Cancer Peter Lee MD Central Ohio Colon & Rectal Center.

Genetics of Colorectal
Cancer
Peter Lee MD
Central Ohio Colon & Rectal Center
Overview
 Molecular biology of cancer
 Epidemiology of colorectal cancer
 Inherited colorectal cancers
 Screening implications of colorectal cancer
 Summary
Cancer is a disease of the cell cycle
“Carcinoma is a genetic disease but it is not necessarily inherited”
Knudsen’s “two hit” hypothesis
Types of genes which may mutate to cause cancer:
 Oncogenes
 Tumor suppressor genes
 DNA repair genes
 p53
Oncogenes
 Cellular oncogene c-onc
 Viral oncogene v-onc
 Proto-oncogene, activated by mutation to
c-onc
Proto-oncogene activation
Tumour suppressor genes
The gene’s normal function is to regulate cell
division. Both alleles need to be mutated or removed
in order to lose the gene activity.
 The first mutation may be inherited or somatic.
 The second mutation will often be a gross event
leading to loss of heterozygosity in the surrounding
area.

Types of proto-oncogene
Growth factor
e.g. SIS oncogene (PDGF)
 G proteins
e.g. ras
 Nuclear transcription factors
e.g. MYC

p53
Suppress progression through the cell cycle in
response to DNA damage
 Initiate apoptosis if the damage to the cell is severe
 Is a transcription factor and once activated, it
represses transcription of one set of genes (several
of which are involved in stimulating cell growth)
while stimulating expression of other genes involved
in cell cycle control

Transformation is a
multistep process
Transformation is a multistep process
DNA Mismatches
 Damage to nucleotides in ds-DNA
 Misincorporation of nucleotide
 Missed or added nucleotides
Acquired DNA Damage
M
-C-A-G-T-
Demethylation
-T-A-G-T-
Nucleotide Misincorporation
-C-A-G-C-T-
CT substitution
-G-T-C-C-A-
-C-A-G-C-T-C-A-G-C-T-
-G-T-C-C-A-
-G-T-T-C-A-
-C-A-G-C-T-G-T-C-C-Acorrectly copied
Added Nucleotides
-C-A-G-C-Tnucleotide added
-G-T-C-C-A-
-C-A-G-C-T-C-A-G-C-T-
-G-T-C C-AA
-G-T-C-C-A-
-C-A-G-C-T-G-T-C-C-Acorrectly copied
Human Mismatch Repair Genes
 MLH1
 PMS1
 PMS2
 MSH2
 MSH3
 MSH6
(3p21)
(2q31-33)
(7p22)
(2p16)
(5q3)
(2p16) (=GT Binding Protein)
Mismatch Repair Genes
 Recognition and repair of mismatches
 Other functions



Repair of branched DNA structures
Prevent recombination of divergent sequences
Direct non-MMR proteins in nucleotide excision
and other forms of DNA repair
Other MMR Proteins
 DNA ligase
 Replication protein A
 Replication factor C
 Proliferating Cell Nuclear Antigen
 Exonucleases
 DNA polymerase 
Defective Mismatch Repair
 Defects in MMR Genes and Function
 Microsatellite Instability
 Cancer development



90% of HNPCC colorectal cancers
20% of sporadic colorectal cancers
30% of sporadic uterine cancers
Cancer Development
 Activation of Oncogenes
 Inactivation
of Tumour Suppressor Genes
 Defects in DNA mismatch repair
 Susceptible to mutation
Genetics of Colorectal
Cancer
Colorectal Cancer
 11% of cancer-
related deaths
 Tumor
progression may
take 10-35 years
 Adenomatous
polyp develops
into carcinoma
Chromosome changes in colorectal cancer
Cancer karyotype
Stable karyotype
Worldwide Statistics for Colorectal
Cancer (CRC)
 875,000 cases in 1996

8.5% of all new cases of cancer
 556,000 deaths
 Incidence rates vary (Up to 20 fold)


Highest in North America, Western Europe,
Australia, New Zealand, Japan
Lowest in India, Northern Africa
Estimated New Cancer Cases of 10
Leading Sites by Gender for the US 2000
Colorectal Cancer Statistics in the
US
• Second overall leading cause of cancer-related
deaths in the US
• Estimated 130,000 new cases and 56,300
deaths in the year 2000
• Declining trends between 1990 and 1996
 Incidence rate: 2.1% per year
 Mortality rates: 1.7% per year
Average Annual Age-Specific US Incidence
and Mortality Rates of CRC, 1992-1996
Prevalence of adenomas
 Age ≥ 50 with any adenomas:
25-40%
 Lifetime risk of cancer at age 50



5% for females
6% for males
Advanced adenomas at highest risk
Risk Factors for Colorectal Cancer
(CRC)






Aging
Personal history of CRC or adenomas
High-fat, low-fiber diet
Inflammatory bowel disease
Family history of CRC
Hereditary colon cancer syndromes
Risk of Colorectal Cancer (CRC)
5%
General population
Personal history of
colorectal neoplasia
15%–20%
Inflammatory
bowel disease
15%–40%
70%–80%
HNPCC mutation
>95%
FAP
0
20
40
60
Lifetime risk (%)
80
100
Familial Risk for CRC
100
70%
80
Lifetime
CRC risk
(%)
60
40
20
2%
6%
8%
10%
17%
0
None
One 1° One 1°
and two
2°
Aarnio M et al. Int J Cancer 64:430, 1995
Houlston RS et al. Br Med J 301:366, 1990
St John DJ et al. Ann Intern Med 118:785, 1993
One 1° Two 1°
age
<45
HNPCC
mutation
Inherited Colorectal
Cancers
Heredity of Colorectal Cancer
 5-8% of all cases of CRC are hereditary
 15-20% are “familial” / multifactorial
 75% of cases are sporadic
Feuer EJ: DEVCAN: National CA Inst. 1999
Causes of Hereditary
Susceptibility to CRC
Sporadic
(65%–85%)
Familial
(10%–30%)
Rare CRC
Hereditary
syndromes
nonpolyposis colorectal
(<0.1%)
Familial adenomatous cancer (HNPCC) (5%)
polyposis (FAP) (1%)
Adapted from Burt RW et al. Prevention and Early Detection of CRC, 1996
Features of Familial CRC
Family history of CRC
with no clear
inheritance pattern
 Age at onset typical of
sporadic CRC
 Multiple causes
 Few or no adenomas

Sporadic
FAP
HNPCC
Rare CRC
syndromes
Familial CRC
Progression of Colorectal Cancer
Loss of
APC
Normal
epithelium
Hyperproliferative
epithelium
Activation Deletion Loss of Other
of K-ras of 18q TP53 alterations
Early
adenoma
Intermediate
adenoma
Adapted from Fearon ER. Cell 61:759, 1990
Late
adenoma
Carcinoma
Metastasis
Adenomatous polyp
 Adenomatous polyp
 Can take 5-10 years for polyp to develop
 Up to 10% of polyps develop into cancer
 Size and histology are risk factors for polyp to
cancer progression
Characteristics of Average Risk
 No well-defined threshold between sporadic
and familial CRC at this time
 Probably safe to include individuals with:


No personal risk factors or family history of CRC
One 2nd or 3rd degree relative with CRC >60 years
with no other family history of CRC
Characteristics of Familial CRC
“Clustering” of colon cancer cases in the family
(age> 50 at diagnosis) without clear dominant
pattern
 One close relative with CRC <60 yrs & family
history does not meet criteria for known
hereditary CRC syndromes
 Likely to be multiple low penetrant genes plus
environmental factors
 Family members warrant earlier CRC screening


Starting at 40 years or 5-10 yrs earlier than age of
diagnosis of the youngest affected relative
Winawer et al., Gastroenterology 2003:124:544-560
Characteristics of Hereditary CRC
 Multiple relatives with colorectal cancer

One or more diagnosed at an early age (<50)
 Sequential generations affected

Except in autosomal recessive syndromes
 Other cancers in the family known to be
associated with CRC (uterine, ovarian, GI)
 Multiple primary tumors or polyps
Hereditary CRC syndromes

Hereditary Non-Polyposis Colorectal Cancer (HNPCC)


Familial Adenomatous Polyposis (FAP)




Variants: Muir-Torre, Turcot
Variants: Gardner, Turcot
Attenuated FAP
APC mutation in Ashkenazi Jews
Others:



Multiple adenomatous polyposis syndrome/MYH gene (MAP)
Peutz-Jeghers syndrome (PJS)
Familial Juvenile Polyposis (FJP)
HNPCC: AKA “Lynch syndrome”

2-3% of all colorectal cancer cases

Autosomal dominant; high penetrance

Typical age of CA onset is 40-50 yrs

Multiple affected generations

60-70% right-sided/proximal CRC tumors

Polyps may be present, multiple primaries common. Can
overlap with AFAP

High lifetime risk of CRC and other cancers beginning age 20
Cancer Risks in HNPCC
100
80
Colorectal 78%
60
% with
cancer 40
Endometrial 43%
Stomach 19%
Biliary tract 18%
Urinary tract 10%
Ovarian 9%
20
0
0
20
40
Aarnio M et al. Int J Cancer 64:430, 1995
60
80
Age (years)
Lifetime cancer risks:
HNPCC
Colorectal
 Endometrial
 Gastric
 Ovarian
 Biliary tract
 Urinary tract
 Small bowel
 Brain/CNS

80%
20-60%
13-19%
9-12%
2%
4%
1-4%
1-3%
Contribution of Gene Mutations
to HNPCC Families
Sporadic
Familial
Unknown 30%
MSH2 30%
HNPCC
Rare CRC
syndromes
FAP
MSH6 (rare) PMS1 (rare)
Liu B et al. Nat Med 2:169, 1996
PMS2 (rare)
MLH1
30%
Amsterdam Criteria (HNPCC)
 3 or more relatives with an HNPCC-related
cancer, one of whom is a 1st degree relative of
the other two
 2 or more successive generations affected
 1 or more cancers diagnosed before age 50
 Failure to meet these criteria
does not exclude HNPCC
Mutations in HNPCC

Caused by mutations or deletions in mismatch repair (MMR)
genes




MSH2, MLH1, MSH6, (PMS2)
90% of detectable mutations in MSH2 and MLH1
50% of families meeting Amsterdam II Criteria have
detectable mutations
Testing/screening options:


Direct genetic testing of MMR genes (in select families)
Initial screening of the tumor tissue by MSI/IHC
When to perform genetic testing
 Family history fulfills Amsterdam II criteria
 Patient has two HNPCC related cancers
or
or
 Patient has CRC and a 1st degree relative with
HNPCC-related cancer, with at least one
cancer diagnosed <50 years of age
 Always test an affected family member first!
Cancer in MSH2 mutation family
Oesophagus
59 yrs
Synchronous
47 years
Colon
39 yrs
Stomach
Rectum
42 yrs
Sarcoma
Mediastinum
27 yrs
Synchronous
41 yrs
Ovary
37 yrs
Synchronous
44 yrs
Endometrial Cancer
Colorectal/Upper GI Cancer
Ovarian Cancer
Other Cancer
Ovary
29 yrs
MSI/IHC screening

Microsatellite Instability (MSI) on tumor tissue


Immunohistochemistry (IHC) on tumor tissue


can be used to screen for HNPCC in select cases
can be used to detect the presence or absence of the mismatch repair
proteins (MSH2, MLH1, etc.)
“Screen positive” individuals can be offered cancer genetic
counseling/assessment and targeted genetic testing
Microsatellite Instability (MSI)


10%–15% of sporadic tumors have MSI
95% of HNPCC tumors have MSI at multiple loci
Normal
Electrophoresis gel
MSI tumor
Criteria for MSI/IHC screening
CRC or endometrial CA <50 yrs
 2 HNPCC cancers in same person
 CRC with “MSI-H histology” diagnosed <60 yrs


Infiltrating lymphocytes, Crohn’s-like lymphocytic
reaction, mucinous/signet ring differentiation,
medullary growth pattern
CRC and one or more 1st degree relative with an
HNPCC-related cancer, one diagnosed <50 yrs
 CRC and two or more 1st or 2nd degree relatives
with HNPCC-related cancers, any age

Umar A et al: J Natl Cancer Inst, 2004; 96(4):261-268
Genetic Testing for
HNPCC Susceptibility
Begin genetic testing with
affected family member
Positive
result
Offer testing to
at-risk family
members
Negative
result
Continued risk of
unidentified familial
mutation
HNPCC Surveillance
 Gene carriers or at-risk relatives:


CRC: colonoscopy age 20-25, repeat 1-2 yrs
Women: gyn exam, endometrial aspiration, TV
U/S, CA-125 (?) age 25-35, repeat 1-2 yrs
 If one HNPCC family member affected w/the
following:


Stomach CA: EGD age 3-35, repeat 1-2 yrs
Urinary tract CA: urine cytology age 30-35, repeat
1-2 yrs
NCCN practice guidelines in oncology – v.1.2003
Diagnostic & Screening Criteria
•
Amsterdam Criteria:
– Exclude FAP
– 3 relatives with CRC
• 1 FDR to other two
– 2 affected generations
– 1 CRC diagnosed <50
Diagnostic
Bethesda Criteria:
– Individual with 2 or
more HNPCC cancers
– CRC or endometrial
cancer dx. < 45
– Adenomas dx. < 40
FAP

Prevalence 0.01%

100’s to 1000’s of colonic adenomas by teens

Cancer risk: colon, gastric, duodenum (periampulla),
small bowel, pancreas, papillary thyroid, childhood
hepatoblastoma

7% risk of CRC by 21 yrs; 93% by 50 yrs

Variants: Gardner, Turcot
Clinical Features of FAP

Estimated penetrance
for adenomas >90%

CHRPE may be present


congenital hypertrophy
of the retinal pigment
epithelium
Untreated polyposis
leads to 100% risk of
cancer
Genetics of FAP

Autosomal dominant inheritance

Caused by mutations in APC tumor suppressor gene
on chromosome 5q

Up to 30% of patients have de novo germline
mutations

Most families have unique mutations

Most mutations are protein truncating

Genotype/phenotype relationships emerging
The APC Tumor Suppressor Gene
Mutations
Codon 1309
5'
1 2 3 4 5 6 7 8 9 10111213 14
3'
15
FAP – surveillance
Colon
 Annual sigmoidoscopy, age 10-12 yrs
 Prophylactic colectomy following polyp detection
w/continued surveillance of rectum, ileal pouch
Duodenal/gastric
 EGD age 25, repeat 1-3 yrs
Gastroenterology 2001; 121: 195. AGA Statement
Genetic Testing: FAP/AFAP

Test an affected family member first!

After genetic counseling and informed consent
APC gene testing can confirm a suspected
diagnosis
 Family members of a person with a known APC
mutation can have mutation-specific testing
 Genetic testing for children at risk for FAP can be
considered before beginning colon screening

Attenuated FAP




20 to 100 polyps, usually more proximal
Onset later than FAP, average age of onset = 50
Lifetime risk of CRC = 80%
Extracolonic tumors occur at same rate as FAP

Not associated with CHRPE

Variant of FAP, mutations in same APC gene

Surveillance:


annual colonoscopy starting late teens or early 20’s
Option of subtotal colectomy
APC gene mutation in
Ashkenazi Jews


Missense mutation (I1307K) associated with increased risk of
CRC and adenomas in Ashkenazi Jews (AJ)
Found in 6% of the general AJ population


12% of AJs with CRC
29% of AJs with CRC and a positive family history

Lifetime risk of CRC in mutation carrier is 10-20%

Screening: colonscopy every 2-5 yrs starting at 35 yrs
MAP syndrome/MYH gene

Multiple adenomatous polyposis (MAP) syndrome





Autosomal recessive; mutations in the MYH gene
Median number of polyps = 55
Mean age of polyp diagnosis = 30-50 years
Small, mildly dysplastic tubular adenomas
Some tubulovillous, hyperplastic, serrated adenomas,
microadenomas
30% of individuals with 15-100 polyps have
homozygous mutations in the MYH gene
 Genetic testing should be offered if >15 polyps (and
APC gene testing negative)

Peutz-Jeghers syndrome
<1% of all CRC cases
Hamartomatous polyps of GI tract as early as 1st
decade
Mucocutaneous hyperpigmentation


lips, mouth, buccal mucosa, fingers
Usually seen in children < 5 yrs
Cancer risk:

colon, small intestine, stomach, pancreas, breast,
ovaries, uterus, testes, lungs, kidneys
Mutations in STK11 gene

found in 70% of familial cases and 30-70% of
sporadic cases
Familial Juvenile Polyposis
<1% of all CRC cases
Autosomal dominant
5 or more juvenile polyps in colon or GI tract

Appear in 1st or 2nd decade

50% lifetime risk of CRC; AOO in 30’s

Increased risk gastric, GI, pancreatic CA
~50% of cases have mutations in either the
MADH4 or BMPR1A genes
Consider Genetics Referral for:
Two or more family members with CRC* at least one <50
Three or more family members w/CRC*; any age
Patient with colon cancer before 40 yrs
Endometrial cancer and family history of CRC <50
Persons with more than one primary CRC <50 yrs or with both
endometrial CA and CRC
Family or personal history of CRC and one or more 1st degree
relative with an HNPCC-related cancer, one diagnosed <50 yrs.
*Same side of family
Consider Genetics Referral for:
MSI and/or IHC tumor results suspicious for HNPCC
Autosomal dominant pattern of cancers in the family
Persons with 15 or more adenomatous colorectal polyps
Persons with multiple hamartomatous or juvenile GI polyps
Persons with a family history of a known hereditary cancer
syndrome
Screening Implications of
Inherited Colorectal
Cancers
Risk of inherited CRC
Risk for CRC based on family history increases with:

Closer degree of relationship and # of affected members

Younger age of onset

Presence of extracolonic tumors, multiple primaries
Family History: Empiric Risks
Lifetime Risk CRC
General population in US
2 to 6%
One 1st degree relative w/CRC
2-3 fold
Two 1st degree relatives w/CRC
3-4 fold
1st degree relative w/CRC <50
3-4 fold
One 2nd or 3rd degree relative w/CRC
1.5-fold
Two 2nd degree relatives w/CRC
2-3 fold
Goal: Classification
Assessment
Risk Classification
Average
Family Hx
Intervention
Standard prevention
recommendations
Moderate
(“Familial”)
Personalized prevention
recommendations
High/Genetic
Referral for genetic evaluation
with personalized prevention
recommendations
CRC Risk Management
Average Risk
1.
No family history CRC OR
2.
One 2nd or 3rd degree relative with CRC
Age to Begin
50 yrs
FOBT annually + Flex sig every 5 yrs; OR
Colonoscopy every 10 yrs; OR
DCBE every 5 yrs
CRC Risk Management
Moderate/Family history
1. Two 1st degree relatives with CRC any age
or one 1st degree relative with CRC < 60
Age to begin
40 years*
Colonoscopy every 5 yrs
2. One 1st degree relative with CRC >60 or
two 2nd degree relatives with CRC any age
Average risk screening
* Or 5-10 yrs earlier than earliest case in family
Gastroenterology: 2003;124:544-560
40 years
Adenoma-Carcinoma Sequence
Accumulation of Mutations
DCC, MCC, p53, K-ras, APC, MSH2, MLH1, etc.
CRC Risk Management
Age to Begin
HNPCC or suspected HNPCC
20-25 yrs
1. Colonoscopy every 1-2 yrs
2. Genetic counseling; consider genetic testing
FAP or suspected FAP
10-12 yrs
1. Flex sig or colonoscopy every1-2 yrs
2. Genetic counseling; consider genetic testing
Chemoprevention

Evidence that ASA, NSAIDs, Calcium, and COX-2 inhibitors
may reduce incidence of CRC by reducing # of adenomas




40-50% risk reduction for developing CRC regardless of location in
colon, age, gender, and race
Generally performed by RCT’s in patients with prior CRC followed for
recurrence of adenomas
Diet, fiber, and antioxidant vitamins have not been shown by
RCT’s to decrease risk of recurrent adenomas
COX-2i’s and Sulindac have been shown to reduce the
number of adenomas found in FAP alone


Not effective for sporadic colon CA
Actually can cause regression of adenomas
Summary
Summary
 Risk factors for colon cancer


Inherited
Acquired (sporadic)-adenomatous polyp, IBD
 Genetic basis for colon cancer


Inherited (FAP, HNPCC, to be defined)
Sporadic polyp-different pathways
Summary
 Genetic counseling and testing


HNPCC
FAP
 Implications for screening/surveillance


Family members
Other malignancies
Thank you!