Colorectal Cancer

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 <50 years
  - FAP – average is 39 years
Sex – M>F

Genetics

All patients with colorectal cancer should be counseled for family history
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 15-20% of sporadic tumors
  - MMR testing should be considered for all patients <50 years; increased likelihood of Lynch syndrome in this age population
- 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 mutation/modification (eg, MLH1, MSH2, MSH6)
- 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 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, 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 young age
- Lynch syndrome – may have multiple tumors
  - 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

Treatment

KRAS (p53), BRAF V600E and PIK3CA exon 20 mutations may indicate low probability of response to EGFR-targeted tyrosine kinase inhibitor therapy (EGFR TKI)
- Genotyping of tumor tissue recommended in order to plan an effective treatment
  - Tissue from previous biopsy acceptable for genotype testing
- PIK3CA mutation is indicative of tumor that may respond to drugs targeted at genes downstream of PIK3CA in the AKT/mTOR-signaling cascade
MMR protein deficiency is predictive of response to therapies using 5-fluorouracil (5-FU)

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 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
- MSI testing for suspected Lynch syndrome
  - MSI also found in 15-20% of sporadic colon cancer
- MMR testing (MLH1, MSH2, MSH6, PMS2)
- KRAS mutation testing
  - Advanced (metastatic) colon cancer patients may benefit from anti-EGFR therapy as monotherapy or combined with chemotherapy
  - All candidates for anti-EGFR therapy should have testing for KRAS mutation (American Society of Clinical Oncology [ASCO] National Comprehensive Cancer Network [NCCN] guideline recommendation)
  - If KRAS mutation is positive in codon 12 or 13, patients may have an inhibited response to anti-EGFR therapy
- BRAF V600E mutation may also be associated with anti-EGFR resistance
- NRAS mutation testing
  - Advanced (metastatic) colon cancer patients may benefit from anti-EGFR therapy as monotherapy or combined with chemotherapy
  - If NRAS mutation positive in codons 12, 13 or 61, patients may have an inhibited response to anti-EGFR therapy
- PIK3CA mutation testing
  - Advanced (metastatic) colon cancer patients may benefit from anti-EGFR therapy as monotherapy or combined with chemotherapy
  - If PIK3CA mutation positive in exon 20, patients may have an inhibited response to anti-EGFR therapy
  - PIK3CA mutational status may indicate a tumor that will respond to drugs targeted at genes downstream of PIK3CA in the AKT/mTOR-signaling cascade
Genetic testing
- Mutation testing for Lynch syndrome
- 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

Histology

Tissue is gold standard for tumor type diagnosis and further testing (MSI, KRAS, NRAS, BRAF)
Immunohistochemistry – potential stains for further diagnosis include CDX2, CEA monoclonal, CEA polyclonal, CK 20, muc-2, muc-4, and p21 (Waf1/Cip 1)

Prognosis

Unstable MSI – suggestive of higher risk for Lynch syndrome with poor 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)
KRAS/NRAS mutations – may predict response to EGFR TKI therapy
PIK3CA mutation – may predict response to EGFR TKI therapy; mutations are associated with a significant increase in colon cancer-specific mortality
IHC markers – p16, p27 (Kip1), and p53 (KRAS)

Differential Diagnosis

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

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, TYMS, and MTHFR
- (5-FU) is a fluoropyrimidine drug used in the treatment of colorectal cancer and other solid tumors
- Pharmacogenetic variations in genes such as DPYD, TYMS, and MTHFR may contribute to risk of toxicity and/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
    - Increased risk of stroke and thromboses in patients ≥65 years
    - Alternative chemotherapeutic agents, therapeutic drug monitoring, altered 5-FU doses, or increased surveillance for adverse drug reactions may be indicated
  - MTHFR mutation detected – associated with decreased MTHFR activity and increased rate of TS reactivity
    - Unknown impact on 5-FU efficacy and toxicity

Hemoccult – fecal blood stool testing
- 50% of documented colon cancers have a negative fecal occult blood test (FOBT)
  - If patient is at risk, consider sigmoidoscopy or colonoscopy even in the presence of a negative FOBT
- Positive FOBT mandates further evaluation (eg, colonoscopy)
Flexible sigmoidoscopy/colonoscopy – negative result does not rule out colorectal cancer
- 90% sensitivity for lesions ≥10 mm
Septin 9
- Biomarker for presence of colorectal cancer; high negative predictive values
- Indicated for individuals ≥50 years who have an average risk of colorectal cancer and no family history of colorectal cancer
- Not intended as substitute for colonoscopy but may be useful as a complement to colonoscopy or for those who are unwilling or unable to have a colonoscopy
  - Patients with elevated levels should undergo colonoscopy to rule out colorectal cancer
- Has been shown to detect cancers from cecum, ascending colon, transverse colon, splenic flexure, descending colon, sigmoid, recto-sigmoid junction, and rectum

Colorectal screening for persons with average risk* (beginning at 50 years)

*Colorectal Screening for Persons with Average Risk (beginning at 50 years)**
Organization	Recommendation
U.S. Preventive Services Task Force (USPSTF); American Academy of Family Practice (AAFP)	50-75 years – one of the following screening regimens** Annual screen for colorectal cancer using FOBT Sigmoidoscopy every 5 years combined with high-sensitivity FOBT every 3 years Colonoscopy every 10 years 76-85 years – recommend against routine screening for colorectal cancer; however, there may be considerations that support colorectal cancer screening in an individual patient >85 years – colorectal cancer screening not recommended
American Cancer Society (ACS)	One of the following regimens** Flexible sigmoidoscopy every 5 years Colonoscopy every 10 years Double-contrast barium enema every 5 years CT colonography every 5 years No upper age limit to discontinue screening
Average risk – age ≥50 years; no history of adenoma or IBD; negative family history (not having one first-degree or two second-degree relatives with colorectal cancer, or a clustering of Lynch syndrome-related cancers in the family) *Patients with a family member diagnosed with colon cancer <60 years should begin colonoscopy screenings every 5-10 years starting at age 40 or 10 years before the age of the youngest family member diagnosed

Serum CEA
- Elevated post-operative titer predicts tumor recurrence
- Pre-operative and post-operative monitoring for changes in concentration
  - Stage II or III tumors – measure every 3 months post-operation, continuing for 3 years
- Patient with metastatic disease – monitoring may help evaluate treatment response
Serum circulating tumor cell count – in metastatic tumors, monitor disease progression and response to therapy
Others
- Serum CA19-9
- Tissue p53
- Deletion 18q – not enough data to recommend its use
- Promising new marker for hereditary colorectal cancers (9q22.2-31.2)

Tests generally appear in the order most useful for common clinical situations

Test name: Mismatch Repair by IHC

ARUP #: 0049302

Methodology: Qualitative Immunohistochemistry

Use:

Preferred test to discriminate between sporadic and hereditary forms of colorectal cancer

Surrogate test for MSI by PCR

May help guide subsequent mutation analysis

Test name: KRAS Mutation Detection with Reflex to BRAF Codon 600 Mutation Detection

ARUP #: 2001932

Methodology: Polymerase Chain Reaction/Pyrosequencing

Use:

May indicate lack of responsiveness to anti-EGFR therapy

Assay detects mutations in codons 12, 13, and 61

If KRAS is not detected, BRAF codon 600 Mutation Detection will be performed

Test name: NRAS Mutation Detection by Pyrosequencing

ARUP #: 2003123

Methodology: Polymerase Chain Reaction/Pyrosequencing

Use:

May indicate lack of responsiveness to anti-EGFR therapy

Test name: Familial Mutation, Targeted Sequencing

ARUP #: 2001961

Methodology: Polymerase Chain Reaction/Sequencing

Use:

Evaluate family members for a known family mutation

A copy of a relative's laboratory test report documenting the gene and specific mutation(s) for which testing is requested must be submitted with the test order

Test name: HNPCC/Lynch Syndrome Deletion/Duplication

ARUP #: 2001728

Methodology: Polymerase Chain Reaction/Multiplex Ligation-dependent Probe Amplification

Use:

Evaluate family members for a known family mutation

Detect mutations and large deletions in MLH1, MSH2, MSH6 or PMS2 genes

Limitations:

For PMS2 testing, suspected deletions or duplication in exons 12-15 require sequencing to exclude pseudogene copy number variants

Test name: Familial Adenomatous Polyposis Panel: APC Sequencing, APC Deletion/Duplication, and MYH 2 Mutations

ARUP #: 2004915

Methodology: Polymerase Chain Reaction/Sequencing/Multiplex Ligation-Dependent Probe Amplification

Use:

Determine genetic basis for FAP

Test at-risk family members with family history but no known familial mutation

Limitations:

Do not use for identification of a known familial mutation

Test name: Familial Adenomatous Polyposis (APC) Sequencing

ARUP #: 2004863

Methodology: Polymerase Chain Reaction/Sequencing

Use:

Detect gene mutations related to APC-associated FAP

Limitations:

Detects ~90% of APC gene mutations

Test name: Familial Adenomatous Polyposis (APC) Deletion/Duplication

ARUP #: 2004920

Methodology: Polymerase Chain Reaction/Multiplex Ligation-Dependent Probe Amplification

Use:

Detect APC deletions and duplications related to APC-associated FAP

Limitations:

Detects APC gene mutations not identified by sequencing

Test name: MYH-Associated Polyposis (MYH) 2 Mutations

ARUP #: 2004911

Methodology: Polymerase Chain Reaction/Sequencing

Use:

Diagnostic or presymptomatic testing for MAP and MUTYH-associated polyposis

Limitations:

Uncertain result means that a gene mutation was detected, it may be pathogenic or benign; clinician should rely on clinical findings and family history

Test name: Septin 9 (SEPT9), Methylated DNA Detection by Real-Time PCR

ARUP #: 2003243

Methodology: Polymerase Chain Reaction

Use:

Screen for colorectal cancer; positive result indicates possible increased risk

Limitations:

Overall sensitivity (all stages) - 90%

Sensitivity (stage I-II) - 87%

Specificity - 89%

Do not use as screening in patients with previous history of colorectal cancer or in patients with family history of early onset colorectal or hereditary colorectal cancer

Test name: Carcinoembryonic Antigen

ARUP #: 0080080

Methodology: Quantitative Electrochemiluminescent Immunoassay

Use:

Monitor tumor recurrence

Limitations:

Not sensitive or specific enough for screening in the general population

Test name: Circulating Tumor Cell Count (Cell Search™)

ARUP #: 0093399

Methodology: Immunomagnetic separation/Immunofluorescence staining/Computer assisted analysis

Use:

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

Results should be interpreted with caution if specimens drawn within 7 days of doxorubicin therapy

Test name: CDX2 by Immunohistochemistry

ARUP #: 2003821