Colorectal Cancer

Diagnosis

Indications for Testing

• Colorectal bleeding; family history of colorectal cancer; clinical symptoms consistent with MAP, FAP, Turcot syndrome, or Gardner syndrome

Laboratory Testing

• Colonoscopy – all polyps should be removed and sent for histology examination
• Molecular testing (on tissue)
  • MSI testing for suspected Lynch syndrome
    • MSI also found in 15-20% of sporadic colon cancer
  • MMR mutation testing (MLH1, MSH2, MSH6, PMS2) – should be guided by immunohistochemistry
  • APC mutation testing
    • Confirm a clinical diagnosis of FAP or attenuated FAP
    • Testing of family member at risk for APC-associated polyposis and no known familial mutation
  • MUTYH testing – for family member at risk for MAP
• Mutation testing to predict the effectiveness of therapies that target the EGFR pathway
  • Presence of one of the following mutations may be associated with an inhibited response to anti-EGFR therapy
    • KRAS
      • 1 of 2 most common mutations associated with inhibited response
      • Individuals who are candidates for anti-EGFR therapy should have testing for KRAS mutation (ASCO, NCCN)
    • BRAF V600E
      • Other most common mutation associated with inhibited response
      • Recommended in nonmutated KRAS cases (NCCN, 2012)
    • NRAS
      • Rare mutation associated with relative resistance
    • PTEN
      • May be associated with relative resistance
    • PIK3CA
      • Exon 20 associated with relative resistance
      • Exons 9 and 20 activating mutations indicate possible response to therapies targeting genes downstream of PI3K in the AKT/mTOR-signaling cascade

Histology

• Tissue is gold standard for tumor classification and further testing (MSI, MMR, KRAS, NRAS, BRAF)
• Immunohistochemistry – stains to guide MMR gene mutation testing
  • MLH1, MSH2, MSH6, PMS2

Prognosis

• Microsatellite unstable (MSI) tumors – generally more favorable prognosis
• Chromosomal alterations in 8p, 17p, 18p – associated with poor prognosis
• Serum markers
  • Carcinoembryonic antigen (CEA) – measure prior to surgery (ASCO)
  • Other potential but not validated serum markers include carbohydrate antigen CA19-9, CA242, CTC, and tissue inhibitor of metalloproteinase-1 (TIMP-1)

Differential Diagnosis

• Diverticulitis
• Inflammatory bowel disease
  • Crohn disease
  • Ulcerative colitis
• Irritable bowel syndrome
• Hemorrhoids/fissures

Screening

Monitoring

Pharmacogenetics and Therapeutic Drug Monitoring

• UGT1A1 genotyping
  • Uridine diphosphate glucuronosyltransferase (UGT1A1) is responsible for clearance of irinotecan, a camptothecin analogue used in treatment of advanced colon cancer
  • Decreased gene expression may lead to drug toxicity (development of severe neutropenia)
    • Two gene variants responsible for 98-99% of genotypes in the Caucasian population – *1  and *28 (repeat TA sequence)
  • Routine reduction of dose in *28 homozygous is not recommended (Evaluation of Genomic Applications in Practice Working Group, 2009) but may identify patients at risk for adverse events and in need of closer monitoring
    • Selective genotyping based on patient preferences
      • Patients homozygous for *1 may tolerate aggressive treatment better than patients with the *28 variant
      • Patients homozygous for *28 may require a dose reduction to minimize dose-related adverse events
• 5-fluorouracil (5-FU) sensitivity – genotyping of DYPD and TYMS
  • 5-FU is a fluoropyrimidine drug used in the treatment of colorectal cancer and other solid tumors
  • Pharmacogenetic variations in genes such as DPYD and TYMS may contribute to risk of toxicity or altered therapeutic benefits
    • DPYD or TYMS mutation detected – predictive of an increased sensitivity to 5-FU and may lead to increased risk for toxicity
      • Alternative chemotherapeutic agents, therapeutic drug monitoring, altered 5-FU doses, or increased surveillance for adverse drug reactions may be indicated

Clinical Background

Colorectal cancer is the third most common form of cancer in the U.S. and can be roughly divided into sporadic, familial and hereditary types.

Epidemiology

• Incidence – 47.9/100,000 (2007 U.S. SEER data)
  • Sporadic – most common form (~80%)
  • Hereditary
    • Hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome – accounts for 2-3% of colon cancer cases in the U.S.
    • Familial adenomatous polyposis (FAP) – occurs in 1/10,000 live births
      • Accounts for <1% of total colon cancers
    • MUTYH (formerly MYH)-associated polyposis (MAP) – rare
    • Others – rare
      • Cowden syndrome (multiple hamartoma syndrome)
      • Peutz-Jeghers syndrome (PJS) – 1/200,000
      • Juvenile polyposis syndrome (JPS) – 1/100,000
      • Hereditary diffuse gastric cancer
• Age 
  • Sporadic – median is 70 years
  • Hereditary – usually <60 years
    • FAP – average is 39 years
• Sex – M>F

Genetics

• Sporadic  
  • TP53 (p53) – mutated in ~75% of sporadic tumors
  • DCC (deleted in colorectal cancers) – mutated in ~70% of colorectal cancers
  • DNA mismatch repair (MMR) gene – mutation or modification found in 15% of sporadic tumors
    • Some authorities recommend MMR testing for all newly diagnosed colorectal carcinoma
  • Hyperplastic polyposis syndrome (HPS) – rarely inherited
• Hereditary
  • Nearly 33% of all colorectal cancer associated with familial clustering
  • Lynch syndrome – associated with microsatellite instability (MSI) and MMR gene mutation/modification (eg, MLH1, MSH2, MSH6, PMS2)
  • FAP
    • Mutations of APC gene – autosomal dominant inheritance, although 25% of cases are de novo
      • Associated with classic FAP and attenuated FAP
      • Also associated with Gardner syndrome, Turcot syndrome (brain tumors) and other extraintestinal manifestations
  • MUTYH-associated polyposis (MAP)
    • MAP is autosomal recessive and occurs due to biallelic mutations in the MUTYH gene
    • Two MUTYH mutations, Y165C and G382D, account for 85% of MAP in Caucasians
  • PJS – mutations of STK11
  • JPS – mutations of SMAD4 or BMPR1A

Risk Factors

• Diet high in animal fats (Western diet)
• Patients with metabolic syndrome
• Inflammatory bowel disease (eg, Crohn, ulcerative colitis)
• Adenoma/sessile serrated polyp (SSP)
• First-degree relative with colorectal adenoma or invasive colorectal cancer
• Ureterosigmoidostomy – carcinoma can develop ≥15 years post procedure

Pathophysiology

• Most colorectal cancers arise from adenomatous polyps
  • Villous adenomas transform into adenocarcinomas more frequently than tubular adenomas
  • Subset of adenocarcinomas develop from hyperplastic-appearing polyps, especially large, right-sided polyps
  • Adenocarcinoma arising in a polyp is considered malignant when it penetrates into the submucosa 
• Other, less-common, tumors can occur (lymphomas, endocrine, mesenchymal)

Clinical Presentation

• Symptoms vary with tumor location – most are located in sigmoid colon and rectum
  • Cecum and ascending colon – tumors may be very large without causing obstruction
    • Anemia is a common presenting symptom
  • Descending and transverse colon – tumors tend to obstruct and cause annular lesions (apple core or napkin ring) with abdominal pain and bloating
  • Rectosigmoid – hematochezia, tenesmus and narrowing of stool caliber
• Sporadic tumors – usually single tumors
• Inherited syndromes – tumors tend to develop at a younger age
  • Lynch syndrome – may have multiple tumors
    • Median age of 61 (10 years younger than sporadic colorectal carcinoma) 
    • For more information, see Lynch syndrome and Lynch syndrome testing algorithm
  • FAP (classic)
    • Affected persons develop hundreds to thousands of colon polyps and subsequent colorectal cancer; often present with multiple tumors; mean age of onset is 39 years
      • Presence of ≥100 polyps is sufficient for clinical diagnosis (or <100 polyps at younger ages in a family with identified FAP)
    • May develop periampullary carcinomas, osteomas, gastric polyps, small intestinal polyps, and tumors of the adrenal gland, liver, thyroid, and pancreas
    • Extraintestinal manifestations in FAP (formerly called Gardner syndrome)
    • Dental abnormalities
    • Polyps of the gastric fundus and duodenum
    • Congenital hypertrophy of the retinal pigment epithelium (CHRPE)
  • FAP (attenuated)
    • <100 adenomas (average is 30); frequently right-sided distribution
    • Cancer appears at older age than classic FAP (mean age >50 years)
    • Individuals with ≥100 polyps at ≥35-40 years may have attenuated FAP
    • Risk of other cancers similar to classic FAP
    • Extraintestinal manifestations of classic FAP are rare
  • MAP
    • 10-100 polyps
    • Mean age of onset is 48-56 years
    • Often indistinguishable from FAP (same extraintestinal manifestations)
  • PJS
    • Perioral melanin pigmentation
    • Increased risk for other cancers (breast, ovary, lung, testes, cervix)
  • JPS
    •  Polyps found mainly in colon

Prevention

• Aspirin and other NSAIDs
  • Suppress cell proliferation by inhibiting prostaglandin synthesis
  • Effects increase with duration of use
• Diets rich in fruit and vegetables
  • Reduces risk but does not reduce incidence of subsequent adenomas in patients with prior adenoma removal
• Estrogens
  • 20-30% reported reduction in colorectal cancer incidence in women who used hormone therapy
  • No mainstream studies proving estrogen therapy is preventative

Indications for Laboratory Testing

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory

Click the plus sign to expand the table of additional tests.

Test Name and Number	Comments
Microsatellite Instability (MSI), HNPCC/Lynch Syndrome, by PCR 0051740 Method: Polymerase Chain Reaction/Fragment Analysis	First-line screening test for LS
HNPCC/Lynch Syndrome (MLH1) Sequencing and Deletion/Duplication 0051650 Method: Polymerase Chain Reaction/Sequencing/Multiplex Ligation-dependent Probe Amplification	Use in MSI carcinoma with suggestive IHC (loss of MLH1 and PMS2 proteins), absence of BRAF codon 600 mutation, and normal MLH1 methylation studies
HNPCC/Lynch Syndrome (MSH2) Sequencing and Deletion/Duplication 0051654 Method: Polymerase Chain Reaction/Sequencing/Multiplex Ligation-dependent Probe Amplification	Use in MSI carcinoma with suggestive IHC (loss of MSH2 and MSH6 proteins)
HNPCC/Lynch Syndrome (MSH6) Sequencing and Deletion/Duplication 0051656 Method: Polymerase Chain Reaction/Sequencing/Multiplex Ligation-dependent Probe Amplification	Use in MSI carcinoma with suggestive IHC (isolated loss of MSH6 protein)
HNPCC/Lynch Syndrome (PMS2) Sequencing and Deletion/Duplication 0051737 Method: Polymerase Chain Reaction/Sequencing/Multiplex Ligation-dependent Probe Amplification	Use in MSI carcinoma with suggestive IHC (isolated loss of PMS2 protein) Suspected deletions or duplications in exons 12-5 require additional sequencing to exclude pseudogene copy number variants
BRAF Codon 600 Mutation Detection with Reflex to MLH1 Promoter Methylation 0051750 Method: Polymerase Chain Reaction/Pyrosequencing	Recommended reflex test for differentiating between LS and sporadic CRC in tumors showing loss of MLH1 If no BRAF mutation is detected, MLH1 promoter methylation is evaluated; evaluation can also help determine whether further workup for HNPCC is indicated
KRAS Mutation Detection 0040248 Method: Polymerase Chain Reaction/Pyrosequencing	Detects most activating KRAS mutations associated with anti-EGFR therapy resistance
5-Fluorouracil (5-FU) Toxicity and Chemotherapeutic Response, 7 Mutations 2007228 Method: Polymerase Chain Reaction/Single Nucleotide Extensions/Fragment Analysis	Detect genetic variants influencing metabolism and action of 5-FU to identify people who may be at risk for drug toxicity
UDP Glucuronosyltransferase 1A1 (UGT1A1) Genotyping 0051332 Method: Polymerase Chain Reaction/Fragment Analysis	Detect irinotecan sensitivity in patients who will be administered these compounds
Solid Tumor Mutation Panel by Next Generation Sequencing 2007991 Method: Massively Parallel Sequencing	Prognosis/treatment of individuals with solid tumor cancers at initial diagnosis or with refractory disease