Colorectal cancer (CRC)

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Colorectal cancer (CRC)

• Professor Yaron Niv
• Rabin Medical Center
• Tel Aviv University

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CRC

• Colon anatomy
• The problem
• Clinical picture
• Diagnosis
• Staging and prognosis
• Etiology/pathogenesis
• Genetic pathways
• Genetic applications

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CRC the problem

• 150,000 new cases every year in USA
• lifetime probability is 6 (death 3)
• Dukes D 5-y-survival 6-12
• Colorectal cancer kills 55,000 Americans every
  year
• 3000 new cases every year in Israel, 1500 deaths

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CRC clinical presentation

• Menwomen 1.21
• Sporadic CRC related to age, rare lt 40y
• Genetic syndromes younger
• Early stages asymptomatic
• Average risk vs. high risk populations
• Symptoms/signs advanced stages
• Abdominal pain, rectal bleeding, weight loss,
  iron deficiency anemia (gtR), change in bowel
  habits (gtL)

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CRC diagnosis (sensitivity/specificity)

• Physical examination
• Rectal examination
• Iron deficiency anemia
• Elevated CEA
• FOBT
• BAE/virtual colonoscopy
• CT/US
• Colonoscopy/sigmoidoscopy

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Dukes Staging

• Dukes 5-year-survival
• A 95
• B 80-85
• C 50-70
• D 6-12

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TNM System - 1958

• T tumor, N nodes,
• M metastasis
• Stage I T1,N0,M0
• Stage IV T1,N1,M1
• Survival
• Treatment
• Clinical trials
• Accurate communication
• Uniform reporting

Grade Well, Moderately well, Poorly
differentiated, Mucinous adenocarcinoma
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Multi-step carcinogenesisproliferation,
differentiation, apoptosis, angiogenesis

• Series of mutational events that release the
  cell from some level of growth restraint,
  followed by waves of clonal expansion of these
  cells.

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Vogelgram
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Genetic definitions - colorectal cancer

• Oncogenes
• Tumor suppressor genes
• DNA repair genes
• Epigenetic processes

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Oncogenes

• Transformed proto-oncogenes
• Signal trasduction and regulation of gene
  expression
• SRC, RAS, MYC, FOS, JUN
• Mutation increases the activity of the encoded
  proteins - proliferation
• Dominantly acting
• JCV, DNA virus encodes for T Ag,
• transform cells of GI tract

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Tumor suppressor genes

• Act in normal tissues to restrain growth and
  maintain the differentiated phenotype.
• Recessively acting one copy undergoes an
  inactivating mutation (heterozygosity - silent),
  the second copy is deleted (loss of
  heterozygosity or LOH - no more protection).
• Tumor specific
• 5q(APC), 17p(P53), 18q(DCC,SMAD)

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Gene silencing prevents translation and
expression and may start tumorigenesis

• Genetic Mutation, deletion, insertion
• TSG (LOH, dominant - 2 hits)
• Oncogene (recessive 1 hit)
• Epigenetic Promoter (CpG island) methylation
  leads to loss of imprinting (LOI)
• When both alleles (maternal and paternal) are
  methylated, imprinting patterns are lost
  carcinogenesis

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DNA methylation in CRC

• Activated by DNA-methyltransferase (uses
  S-adenosyl methionine) adds CH3 to Cytosine
  followed by Guanine (CpG island)
• MLH1 hypermethylation is responsible for up to
  80 of MSI tumors
• Therapeutic potential
• 1. Inhibition by 5-deoxy-azacytidine
• 2. MSI-H tumors are resistant to
• 5FU-based chemotherapy

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Microsatellite instability (MSI H)

• Stretches of DNA a short motif (1-5
  nucleotides) is repeated several times
• Mutation (germ-line or somatic) or
  hypermethylation (somatic, epigenetic) of DNA
  repair gene (MLH1)
• Diagnosis genotyping fluorescently labeled PCR
  products with the use of an automated sequencer
• A panel of 5 microsatellite markers MSI-H 2
  or more of them is a positive result

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Genomic instability in CRC

• 50 - Suppressor pathway - chromosomal
  instability (CIN, LOH)
• 15 - Mutator pathway -
• microsatellite instability (MSI)
• 35 - CpG island methylation phenotype of TSG
  (CIMP)

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Colorectal cancer
50
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Chromosomal instability (CIN) LOH,
aneuploidy Predominantly Lt. sided Highly
differentiated Little lymphocytic
infiltration Rarely mucinous Worse prognosis
MSI-H Diploidy Predominantly Rt. Sided Poorly
differentiated Lymphocytic infiltration Often
mucinous Better prognosis
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CpG island methylator phenotype (CIMP)
35 Serrated adenoma pathway Rt, women, old, BRAF
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HNPCC
Epigenetic silencing of MLH1
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Genetic applications

• Diagnosis of genetic (germ line) syndromes
• Diagnosis (screening) of sporadic CRC
• Prognosis of sporadic CRC

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Distribution of CRC ()
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FAP

• Hundreds to thousands of adenomas at the age of
  16, CRC risk 100 (39y)
• Gardner, AAPC, Turcot
• Annual sigmoidoscopy start at age 10-12y

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FAP, Extra-Colonic Cancers, Lifetime risk ()
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Hereditary NonPolyposis Colorcetal Cancer

• Amsterdam II criteria 3 1st degree relatives
  with CRC (female genitalia, other GI), 2
  generations,
• 1 case lt 50 y
• LOH of DNA mismatch repair genes
• Microsatellite instability
• Proximal colon, fast growing adenomas, better
  prognosis, relatively resistant to chemotherapy
• CRC risk 80
• Colonoscopy every 2y, start age 25y or 10 years
  younger the earliest case

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HNPCC, Extra-Colonic Cancers - Lifetime Risk ()
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Stool DNA quantitationLoktinov, Clin Caner Res
984337

• Normal cells - apoptosis - short DNA
• Cancer cells - necrosis - long DNA
• 17 CRC - 2133?407 ng/ml
• 28 healthy - 469? 65 ng/ml
• p0.0005

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Tumor MSI status predictor of benefit from
5-FU-based adjuvant chemotherapy for CRCRibic, N
Engl J Med 2003349247

• 570 patients CRC tissue specimens
• MSI-H MSS
• N 95 475
• 5-y-s 78 72
• No adjuvant 88 68
• Adjuvant 71 76