Colorectal Cancer

Clinical Background

Colorectal cancer is second only to lung cancer as a cause of cancer-related deaths in the U.S.

Epidemiology

Incidence – 34/100,000, according to U.S. SEER (Surveillance Epidemiology and End Results) database
Age – usually ≥50 years
Sex – M>F

Inheritance

Microsatellite instability (MSI) (the expansion or contraction of short nucleotide repeats) is seen in tumors associated with Lynch syndrome (HNPCC) as well as in 10-15% of sporadic colorectal cancers
- MSI can be determined directly by PCR or indirectly by immunohistochemistry (IHC) for mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2)
  - Hypermethylation of the MLH1 promoter is the cause of instability in most sporadic microsatellite-unstable colorectal cancers
    - The most common IHC profile for a sporadic microsatellite-unstable cancer will be abnormal MLH1/PMS2 immunostaining
    - Lynch-associated tumors will also show this IHC profile due to a germline mutation in MLH1
    - IHC can also be used as a guide for subsequent germline mismatch repair gene evaluation
- Most sporadic microsatellite-unstable colorectal cancers also harbor mutations in the oncogene BRAF
  - Because the BRAF V600E mutation and MLH1 methylation are commonly seen in sporadic microsatellite-unstable colorectal cancers, and are only rarely seen in Lynch syndrome, these two features can be used to help distinguish between sporadic and Lynch-associated tumors with the IHC profile of abnormal MLH1/PMS2
    - BRAF V600E mutations can also be used to evaluate the effectiveness of therapy with epidermal growth factor receptor (EGFR) inhibitors
  - BRAF V600E mutations are also seen in papillary carcinoma of the thyroid

Risk Factors

Diet high in animal fats (Western diet)
Patients with metabolic syndrome
Genetics – hereditary syndromes (autosomal dominant transmission)
- Familial adenomatous polyposis (FAP)
  - Autosomal dominant syndrome in which affected persons develop hundreds to thousands of colon polyps and subsequent colorectal cancer
  - Occurs in 1/20,000 live births and accounts for <1% of total colon cancers
  - Usually caused by mutations in the APC gene, a tumor-suppressor gene on chromosome 5
  - Can also be associated with brain tumors (Turcot syndrome) and other extraintestinal manifestations
    - May develop periampullary carcinomas, osteomas, gastric polyps, small intestinal polyps, and tumors of the adrenal gland, liver, and thyroid
    - Extraintestinal manifestations in FAP, formerly called Gardner syndrome
- Hereditary nonpolyposis colorectal cancer (HNPCC) or Lynch syndrome
  - Most common form of inherited colorectal cancer
    - Accounts for 2-3% of colon cancer cases in the U.S.
    - Autosomal dominant; 80% will develop colorectal cancer
  - Patients are also at risk for developing tumors in the uterus (endometrial cancer – 20-60% risk), ovaries (12% risk), stomach, small bowel, hepatobiliary system, pancreas, renal pelvis and ureter
  - Associated with underlying germline mutations in DNA mismatch repair genes MLH1, MSH2, MSH6 and PMS2
    - 1-2% of colorectal cancer due to mutations in mismatch repair genes
- Hamartomatous polyps
  - Peutz-Jeghers syndrome
  - Juvenile polyposis
  - Cowden syndrome
Other risks
- Ureterosigmoidostomy – carcinoma can develop ≥15 years post procedure

Pathophysiology

Most colorectal cancers arise from adenomatous polyps
- Villous adenomas transform into adenocarcinomas three times 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 and mesenchymal tumors)

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 obstructing
  - 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

Prevention

Aspirin and other NSAIDs
- Suppress cell proliferation by inhibiting prostaglandin synthesis
- Effects increase with duration of use
Diets rich in fruit and vegetables
- Reduce risk
- Do not reduce incidence of subsequent adenomas in a patient 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

Diagnosis

Colorectal cancer
- Indications for testing – colorectal bleeding; family history of colorectal cancer
- Laboratory testing
  - Hemoccult – stool testing
  - Histology – tissue biopsy of any abnormal surfaces of a polyp
  - Imaging studies
    - Colonoscopy – negative result does not rule out colorectal cancer
    - Virtual colonoscopy
MSI
- Indications for testing – early onset of colorectal cancer or family history associated with colorectal cancer in multiple family members
- Laboratory testing
  - Work-up of Lynch syndrome is facilitated by identification of MSI in the tumor, either directly by PCR or indirectly by IHC evaluation of mismatch repair proteins
- Amsterdam criteria, formerly used to assess familial risk for HNPCC, are now considered obsolete
  - Approximately 50% of patients with DNA mismatch repair mutations did not meet Amsterdam criteria; conversely, only 50% of patients who did meet the criteria had a mismatch repair mutation
- The revised Bethesda guidelines are now considered to be more relevant

Revised Bethesda Guidelines for Testing Colorectal Tumors for MSI

Tumors from individuals should be tested for MSI in the following situations:

Colorectal cancer diagnosed in a patient who is <50 years of age
Presence of synchronous, metachronous colorectal, or other HNPCC-associated tumors^a, regardless of age
Colorectal cancer with MSI-H^b histology^c diagnosed in a patient who is <60 years of age^d
Colorectal cancer diagnosed in one or more first-degree relatives with an HNPCC-related tumor, with one of the cancers being diagnosed in patient <50 years
Colorectal cancer diagnosed in two or more first- or second-degree relatives with HNPCC-related tumors, regardless of age

^a HNPCC-related tumors include colorectal, endometrial, stomach, ovarian, pancreas, ureter and renal pelvis, biliary tract, and brain (usually glioblastoma as seen in Turcot syndrome) tumors, sebaceous gland adenomas and keratoacanthomas in Muir-Torre syndrome, and carcinoma of the small bowel

^b MSI-H = high MSI in tumors refers to changes in two or more of the five National Cancer Institute-recommended panels of microsatellite markers

^c Presence of tumor infiltrating lymphocytes, Crohn-like lymphocytic reaction, mucinous/signet-ring differentiation, or medullary growth pattern

^d There was no consensus among the workshop participants on whether to include the age criteria in guideline 3 above; participants voted to keep <60 years of age in the guidelines

Prognosis

Serum markers
- Carcinoembryonic antigen (CEA)
- Other potential but not validated serum markers include carbohydrate antigen CA19-9, cancer antigen CA242 and tissue inhibitor of metalloproteinase-1 (TIMP-1)
Tissue markers
- Mutation of KRAS or BRAF genes indicates low probability of response to EGFR-directed drugs

Differential Diagnosis

Diverticulitis
Inflammatory bowel disease
Irritable bowel syndrome
Hemorrhoids/fissures

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

Test Name and Number	Recommended Use	Limitations
MLH1 Full Gene Analysis 0051650 Method: Polymerase Chain Reaction/Sequencing/Multiplex Ligation Probe Amplification	Detect mutations and large deletions in MLH1 gene
HNPCC/Lynch Syndrome (MSH2) Sequencing and Deletion/Duplication 0051654 Method: Polymerase Chain Reaction/Sequencing/Multiplex Ligation Probe Amplification	Detect mutations and large deletions in MSH2 gene	Rare diagnostic errors can occur due to primer and probe site mutations Breakpoints of large deletions/duplications will not be determined Regulatory region mutations, deep intronic mutations and mutations in genes other than MSH2 will not be detected
MSH6 Full Gene Analysis 0051656 Method: Polymerase Chain Reaction/Sequencing/Multiplex Ligation Probe Amplification	Detect mutations and large deletions in MSH6 gene
HNPCC/Lynch Syndrome (PMS2) Sequencing and Deletion/Duplication 0051737 Method: Polymerase Chain Reaction/Sequencing/Multiplex Ligation-dependent Probe Amplification	Detect mutations and large deletions in PMS2 gene
HNPCC/Lynch Syndrome, Microsatellite Instability by PCR 0051740 Method: Polymerase Chain Reaction/Fragment Analysis	Determine whether tumor is microsatellite stable or unstable for Lynch syndrome work-up
Microsatellite Instability/HNPCC by Immunohistochemical Stain 0049302 Method: Immunohistochemistry	Surrogate test for MSI and may help guide subsequent mutation analysis
Immunohistochemistry Stain Offering arup005 Method: Immunohistochemistry	For fixed tissue samples, consultative services as well as immunohistochemical staining for CEA, CK20, Muc-1, Muc-2 Glycoprotein, p16, p21, CDX2, p27, p53, MSI/HNPCC, and EGFR pharmDX™ are available
BRAF V600E Mutation with Reflex to MLH1 Promoter Methylation, Paraffin 0051750 Method: Polymerase Chain Reaction/Fluorescence Resonance Energy Transfer Analysis	Determine whether further work-up for Lynch syndrome is necessary Assist in determining whether therapy with EGFR inhibitors will be effective If no BRAF mutation is detected, MLH1 promoter methylation is evaluated; evaluation can also help determine whether further workup for HNPCC is indicated	Mutations other than BRAF V600E will not be detected <10-20% presence of a mutant allele may not be detected
BRAF V600E Mutation Detection by PCR 2002498 Method: Polymerase Chain Reaction/Fluorescence Monitoring	Evaluation for this mutation can also help determine the effectiveness of therapy with EGFR inhibitors BRAF V600E mutations are also seen in papillary carcinomas of the thyroid
Familial Mutation, Targeted Sequencing 2001961 Method: Polymerase Chain Reaction/Sequencing	Evaluate family members for a known family mutation in a mismatch repair gene
HNPCC/Lynch Syndrome Deletion/Duplication 2001728 Method: Polymerase Chain Reaction/Multiplex Ligation-dependent Probe Amplification	Detect mutations and large deletions in MLH1, MSH2, MSH6 or PMS2 genes
Carcinoembryonic Antigen 0080080 Method: Eletrochemiluminescent Immunoassay	Monitor tumor recurrence	Not sensitive or specific enough for screening in the general population
Circulating Tumor Cell Count (Cell Search™) 0093399 Method: Immunomagnetic separation/Immunofluorescence staining/Computer assisted analysis	Use in metastatic tumors in conjunction with clinical data and imaging Monitor disease progression and response to therapy when comparing baseline values to serially monitor response and assess prognosis Prognostic marker that provides information about progression-free survival and overall survival
KRAS Mutation Detection with BRAF reflex 2001932 Method: Polymerase Chain Reaction/Pyrosequencing/Fluorescence Resonance Energy Transfer	Use in metastatic tumors; helps predict response to EGFR-directed therapy

Additional Tests Available

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

Test Name and Number	Comments
KRAS Mutation Detection 0040248 Method: Polymerase Chain Reaction/Pyrosequencing	For use in metastatic tumors; helps predict response to EGFR-directed therapy
5-Fluorouracil Sensitivity (DYPD, TYMS & MTHFR) 8 Mutations 2002420 Method: Polymerase Chain Reaction/Primer Extension	Use to detects genetic variants influencing metabolism and action of 5-FU to identify people that may be at risk for drug toxicity
UDP Glucuronosyltransferase 1A1 (UGT1A1) Genotyping 0051332 Method: Polymerase Chain Reaction/Fragment Analysis