• Differentiate hereditary nonpolyposis colorectal cancer (HNPCC) from non-HNPCC colorectal cancer (CRC)

• Assess risk of HNPCC in family members of individuals with HNPCC

HNPCC, which accounts for about 3% to 5% of CRCs, is caused by defects in mismatch repair (MMR) enzymes. These defects may also increase the risk of endometrial, cervical, stomach, ovarian, and other forms of cancer. About 90% of individuals with HNPCC have mutations in 1 of 2 MMR genes, MLH1 or MSH2,¹ and mutations in MSH6, PMS1, and PMS2 have also been implicated.

HNPCC is an autosomal dominant condition with variable penetrance. Individuals with HNPCC typically inherit 1 copy of a defective MMR allele; mutations in somatic tissue may cause loss of the normal allele, leading to an increased rate of mutations in affected cells. Mutations in oncogenes or tumor suppressor genes then lead to carcinogenesis. The lifetime risk of CRC in individuals with an MMR gene mutation is about 80%.²

Diagnosis of HNPCC is based on clinical features and familial cancer patterns,^3,4 or on detection of mutations in MMR genes. Although HNPCC appears to have a slightly more favorable prognosis than non-HNPCC CRC, the often rapid progression from adenomatous polyps to malignant lesions necessitates aggressive follow up for individuals with HNPCC and their first-degree relatives; close surveillance of family members can reduce the rate of CRC and overall mortality by >60%.^5,6 Detection of MMR mutations is important for counseling individuals with HNPCC and their families, as family members without a known familial mutation are at the same risk as the general population and do not require intensive screening.

If a familial mutation is not known, testing suspected HNPCC tumors for microsatellite instability (MSI) can help determine the need for MMR mutation analysis. Microsatellites are regions of repetitive DNA with repeating units of 1 to 7 base pairs. These regions are prone to replication errors, which can be detected as heterogeneous repeat numbers at specific microsatellite regions. Because MMR enzymes normally repair such errors, detection of MSI in tumor tissue suggests the presence of MMR defects. MSI is found in most HNPCCs, but only about 15% of sporadic colorectal tumors.

Because of the relative frequencies of MMR mutations, MLH1 and MSH2 should be examined first; if no mutations are found, mutations in MSH6 should be sought. If the family mutation is known, only the relevant exon in the affected gene should be tested.

• Individuals with CRC who meet the Amsterdam criteria for diagnosis of HNPCC³

• Individuals with documented MSI in a colorectal tumor

• First-degree relatives of individuals who have a known MMR mutation

• If the familial MMR mutation is not known: first-degree relatives of individuals who

  ■   Meet the Amsterdam criteria or

  ■   Have 2 HNPCC-related cancers, including synchronous and metachronous CRCs or
       associated extracolonic cancers (endometrial, ovarian, gastric, hepatobiliary or small bowel
       cancer or transitional cell carcinoma of the renal pelvis or ureter) or

  ■   Have CRC and have a first-degree relative with CRC and/or HNPCC-related extracolonic cancer
       and/or a colorectal adenoma; one of the cancers diagnosed at age <45 years, and the adenoma
       diagnosed at age <40 years⁹

5 mL whole blood in a lavender-top (EDTA) tube or yellow-top (ACD) tube; 3 mL minimum. Ship at room temperature; do not freeze.

Alternatively, submit extracted DNA (≥7 μg) in TE or sterile water. Ship refrigerated.

• Polymerase chain reaction (PCR) amplification of MMR gene regions

• Sequence analysis of both strands of each amplified product

• Automated fluorescent detection

• Report lists nucleotide changes in coding sequences and known splice sites

• Analytical sensitivity: >98%

• Analytical specificity: detection of heterozygous point mutations, small deletions, and insertions in relevant MMR gene

• Aliases: Lynch Syndrome Mutation; HNPCC Mismatch Repair Gene Mutation

CPT Codes*

No mutations detected

Individuals with CRC: Detection of an MMR gene mutation in an individual with colon cancer suggests the need for aggressive screening for recurrent CRC and, possibly, other cancers associated with HNPCC (eg, endometrial and ovarian cancer). American Gastroenterological Association (AGA) guidelines recommend colonoscopy every 1 to 2 years for individuals with a clinical or genetic diagnosis of HNPCC.⁶ Genetic counseling should be offered to the patient and first-degree family members, who may benefit from germline mutation testing.

If mutations are not found in MLH1 or MSH2, mutations in MSH6 should be sought. Mutations not identified in these assays may also be associated with HNPCC.

At-risk family members: If the familial mutation is known, detection of that mutation implies an increased risk of HNPCC and associated cancers. AGA guidelines recommend colonoscopy every 1 to 2 years for those at increased risk of HNPCC, beginning at age 20 to 25, or 10 years before the earliest age of CRC diagnosis in the family.⁶ Individuals without the mutation are not at increased risk and can be followed up according to screening recommendations for the normal-risk population. If the familial mutation is not known, negative MLH1 and MSH2 findings should be followed with tests for mutations in MSH6.