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

2. Overview Molecular biology of cancer Epidemiology of colorectal cancer
Inherited colorectal cancers
Screening implications of colorectal cancer
Summary

3. Cancer is a disease of the cell cycle
Cells either grow and divide with restraint ...or not! The many kinds of malignant growth that the term "cancer" represents all have one lethal attribute in common:
The cells of the malignancy go through the cell cycle without restraint.
These cells "defy" the control mechanisms that lie with them.
What Is the Connection Among Cancer, the Cell Cycle, and Genetics?
There are many protein molecules involved in the cell cycle, each is the product of a single gene. When there is a mutation in one of these genes, it can:
increase the likelihood that a cell will become cancerous and eventually, through repeated, unrestrained division, overtake the normal cells, become malignant; and
possibly spread, or metastasise throughout the body.
Cancer can develop at almost any stage in life. There are some forms of cancer that develop very early, such as retinoblastoma (a cancer of the eye); others tend to develop in childhood, such as various forms of leukaemia, a cancer of the blood; and, of course, there are many forms that develop during adulthood.
In each case, cancer is the result of a mutated gene, or a series of mutated genes, that lead to unregulated cell growth and haphazard controls over cell proliferation.
“Carcinoma is a genetic disease but it is not necessarily inherited”

4. Knudsen’s “two hit” hypothesis

5. Types of genes which may mutate to cause cancer:
Oncogenes
Tumor suppressor genes
DNA repair genes
p53

6. Oncogenes Cellular oncogene c-onc Viral oncogene v-onc
Proto-oncogene, activated by mutation to c-onc

7. Proto-oncogene activation

8. 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.

9. Types of proto-oncogene
Growth factor e.g. SIS oncogene (PDGF)
G proteins e.g. ras
Nuclear transcription factors e.g. MYC

11. 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

12. Transformation is a multistep process

13. Transformation is a multistep process

14. DNA Mismatches Damage to nucleotides in ds-DNA
Misincorporation of nucleotide
Missed or added nucleotides

15. Acquired DNA Damage M
-C-A T-A-
-G-T G-T-
Demethylation

16. Nucleotide Misincorporation
-C-A-G-C-T-
-G-T-C-C-A-
CT substitution
-C-A-G-C-T-
-G-T-T-C-A-
-G-T-C-C-A-
-C-A-G-C-T-
-G-T-C-C-A-
correctly copied

17. Added Nucleotides -C-A-G-C-T- -G-T-C-C-A- -C-A-G-C-T- -G-T-C C-A-
correctly copied
nucleotide added
-C-A-G-C-T-
-G-T-C-C-A-

18. Human Mismatch Repair Genes
MLH1 (3p21)
PMS1 (2q31-33)
PMS2 (7p22)
MSH2 (2p16)
MSH3 (5q3)
MSH6 (2p16) (=GT Binding Protein)

19. 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

20. Other MMR Proteins DNA ligase Replication protein A
Replication factor C
Proliferating Cell Nuclear Antigen
Exonucleases
DNA polymerase 

21. 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

22. Cancer Development Activation of Oncogenes
Inactivation of Tumour Suppressor Genes
Defects in DNA mismatch repair
Susceptible to mutation

23. Genetics of Colorectal Cancer

24. Colorectal Cancer 11% of cancer-related deaths
Tumor progression may take years
Adenomatous polyp develops into carcinoma

25. Chromosome changes in colorectal cancer
Cancer karyotype
Stable karyotype

26. 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

27. Estimated New Cancer Cases of 10 Leading Sites by Gender for the US 2000

28. 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

29. Average Annual Age-Specific US Incidence and Mortality Rates of CRC, 1992-1996

30. Prevalence of adenomas
Age ≥ 50 with any adenomas: %
Lifetime risk of cancer at age 50
5% for females
6% for males
Advanced adenomas at highest risk

31. 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 2

32. Risk of Colorectal Cancer (CRC)
General population 5%
Personal history of colorectal neoplasia
15%–20%
Inflammatory bowel disease
15%–40%
70%–80%
HNPCC mutation
>95%
FAP 20 40 60 80
100
Lifetime risk (%) 3

33. Familial Risk for CRC Lifetime CRC risk (%) 70% 17% 10% 6% 8% 2% None
One 1° and two 2°
One 1° age <45
Two 1°
HNPCC mutation
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

34. Inherited Colorectal Cancers

35. Heredity of Colorectal Cancer
5-8% of all cases of CRC are hereditary
15-20% are “familial” / multifactorial
75% of cases are sporadic
~75% of cases of CRC are sporadic
only 7% of sporadic cases occur <55
~15-20% are “familial” / multifactorial – genetic testing not generally available for low penetrance genes associated with increased risk of CRC
~5-8% are hereditary (defined cancer susceptibility syndromes caused by single genes)
Feuer EJ: DEVCAN: National CA Inst. 1999

36. Causes of Hereditary Susceptibility to CRC
Sporadic (65%–85%)
Familial (10%–30%)
Rare CRC syndromes (<0.1%)
Hereditary nonpolyposis colorectal cancer (HNPCC) (5%)
Familial adenomatous polyposis (FAP) (1%)
Adapted from Burt RW et al. Prevention and Early Detection of CRC, 1996

37. 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
Familial CRC
FAP
HNPCC
Rare CRC syndromes

38. Progression of Colorectal Cancer
Loss of
APC
Activation
of K-ras
Deletion of 18q
Loss of
TP53
Other
alterations
Normal
epithelium
Hyper-
proliferative
epithelium
Early
adenoma
Inter-
mediate
adenoma
Late
adenoma
Carcinoma
Metastasis
Adapted from Fearon ER. Cell 61:759, 1990

39. 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

40. 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

41. 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:

42. 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

43. Hereditary CRC syndromes
Hereditary Non-Polyposis Colorectal Cancer (HNPCC)
Variants: Muir-Torre, Turcot
Familial Adenomatous Polyposis (FAP)
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)

44. HNPCC: AKA “Lynch syndrome”
2-3% of all colorectal cancer cases
Autosomal dominant; high penetrance
Typical age of CA onset is 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
Typical age of onset is 40-50, range from yrs
Preponderance of right-sided/proximal tumors – 60%
Polyps may be present (usually few to < 100), multiple primaries common. Can overlap AFAP so consider this diagnosis if >20 colon polyps detected.

45. Cancer Risks in HNPCC 100 80 60 % with cancer 40 20 20 40 60 80
Colorectal 78% 60
% with cancer
Endometrial 43% 40
Stomach 19% 20
Biliary tract 18%
Urinary tract 10%
Ovarian 9% 20 40 60 80
Age (years)
Aarnio M et al. Int J Cancer 64:430, 1995

46. Lifetime cancer risks: HNPCC
Colorectal %
Endometrial %
Gastric %
Ovarian %
Biliary tract %
Urinary tract %
Small bowel %
Brain/CNS %
Cancer Risk with HNPCC:
CRC - 80% lifetime,
40% for 2nd primary

47. Contribution of Gene Mutations to HNPCC Families
Sporadic
Familial
Unknown 30%
MSH2 30%
HNPCC
Rare CRC syndromes
FAP
MLH1
30%
MSH6 (rare)
PMS1 (rare)
PMS2 (rare)
Liu B et al. Nat Med 2:169, 1996

48. 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

49. 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
Autosomal dominant condition caused by mutations in one of a number of mismatch repair genes
MSH2, MLH1, MSH6, PMS1, or PMS2, others(?)
Sequencing of the MSH2 and MLH1 genes can identify up to 60-70% of HNPCC
Microsatellite Instability (MSI) and Immunohistochemistry (IHC) testing on tumor tissue can be used to screen for possible HNPCC
Genetic testing should be done on an affected family member, only after genetic counseling and informed decision-making

50. When to perform genetic testing
Family history fulfills Amsterdam II criteria or
Patient has two HNPCC related cancers 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!

51. Cancer in MSH2 mutation family
Endometrial Cancer Colorectal/Upper GI Cancer
Ovarian Cancer Other Cancer

52. MSI/IHC screening Microsatellite Instability (MSI) on tumor tissue
can be used to screen for HNPCC in select cases
Immunohistochemistry (IHC) on tumor tissue
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

53. Microsatellite Instability (MSI)
10%–15% of sporadic tumors have MSI
95% of HNPCC tumors have MSI at multiple loci
Normal
MSI tumor
Electrophoresis gel

54. 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):

55. Genetic Testing for HNPCC Susceptibility
Begin genetic testing with
affected family member
Positive result
Negative result
Offer testing to at-risk family members
Continued risk of unidentified familial mutation

56. 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

57. •
Diagnostic
Screening

58. 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

59. 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

60. 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

61. The APC Tumor Suppressor Gene Mutations
Codon 1309 5' 3' 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

62. 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

63. 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
APC gene analysis (either by protein truncation testing [PTT] or sequencing) can confirm a suspected diagnosis
PTT detects 80-90% of affected persons (FAP)
Gene sequencing detects up to 95% of affecteds
Family members of a person with a known APC mutation can be tested for carrier status
Testing at-risk children – can be considered before beginning screening (10-12yrs)
Detection rate for AFAP is not known

64. 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
Option of subtotal colectomy if polyps too numerous – AFAP does not generally affect the rectum, although continued surveillance is recommended.

65. 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

66. 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 = years
Small, mildly dysplastic tubular adenomas
Some tubulovillous, hyperplastic, serrated adenomas, microadenomas
30% of individuals with polyps have homozygous mutations in the MYH gene
Genetic testing should be offered if >15 polyps (and APC gene testing negative)

67. 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

68. 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

69. 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
Any patient with 2 or more family members (same side) with early onset CRC (<50 yrs)
Any colon cancer case before 40 yrs
Woman with endometrial cancer <45 and family history of early onset CRC
Persons with more than one primary CRC <50 yrs or with both endometrial and CRC
Autosomal dominant pattern of cancers in the same lineage
Insurance coverage: Some insurers and some plans will cover cancer genetic risk assessment/cancer genetic counseling. Others will not. More difficult to obtain coverage for unaffected person with a family history than an affected person. Pre-authorization recommended.
Pre-authorization for cancer genetic testing is important as tests are expensive. The genetic counselor will facilitate the pre-auth for testing if indicated and if patient decides to have testing.
Insurance discrimination – needs to be discussed before insurer is contacted regarding coverage.

70. 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

71. Screening Implications of Inherited Colorectal Cancers

72. 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
About 10% of all people have a 1st degree relative with CRC, which increases risk 2-fold
Risk for CRC increases with:
degree of relationship and # of affected members
younger age of onset
presence of extracolonic tumors, multiple primaries

73. 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 < fold
One 2nd or 3rd degree relative w/CRC 1.5-fold
Two 2nd degree relatives w/CRC 2-3 fold

74. Goal: Classification Assessment Risk Classification Intervention
Standard prevention
recommendations
Average
Moderate
(“Familial”)
Personalized prevention
recommendations
Family Hx
Referral for genetic evaluation
with personalized prevention
recommendations
High/Genetic

75. CRC Risk Management Age to Begin Average Risk 50 yrs
No family history CRC OR
One 2nd or 3rd degree relative with CRC
ACBE = air contrast barium enema. FOBT = fecal occult blood test
FOBT annually + Flex sig every 5 yrs; OR
Colonoscopy every 10 yrs; OR
DCBE every 5 yrs

76. Average risk screening
CRC Risk Management
Moderate/Family history Age to begin
1. Two 1st degree relatives with CRC any age 40 years*
or one 1st degree relative with CRC < 60
2. One 1st degree relative with CRC >60 or 40 years
two 2nd degree relatives with CRC any age
* Or 5-10 yrs earlier than earliest case in family
Colonoscopy every 5 yrs
Average risk screening
Gastroenterology: 2003;124:

77. Adenoma-Carcinoma Sequence Accumulation of Mutations DCC, MCC, p53, K-ras, APC, MSH2, MLH1, etc.

78. CRC Risk Management Age to Begin HNPCC or suspected HNPCC 20-25 yrs
FAP or suspected FAP yrs
Colonoscopy every 1-2 yrs
Genetic counseling; consider genetic testing
Flex sig or colonoscopy every1-2 yrs
Genetic counseling; consider genetic testing

79. 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

80. Summary

81. Summary Risk factors for colon cancer Genetic basis for colon cancer
Inherited
Acquired (sporadic)-adenomatous polyp, IBD
Genetic basis for colon cancer
Inherited (FAP, HNPCC, to be defined)
Sporadic polyp-different pathways 

82. Summary Genetic counseling and testing
HNPCC
FAP
Implications for screening/surveillance
Family members
Other malignancies

83. Thank you!