Hereditary Colon Cancer Related Genetic Tests
Most colorectal cancer (CRC) are likely caused by lifestyle factors and
old age. However, approximately 15-30% of all CRC cases are an
inherited genetic disorders. Recent studies have been shown that the
inherited genetic disorders that can cause CRC include familial
adenomatous polyposis (FAP) and hereditary non-polyposis colorectal
cancer (HNPCC) (also called Lynch syndrome)
■ Familial adenomatous polyposis(FAP)
FAP develop hundreds to thousands of colorectal polyps, small
abnormalities at the surface of the intestinal tract, especially in the
colon or rectum. It can also develop silently giving few or no signs until it has developed into colorectal cancer. FAP are caused by APC gene
defects on chromosome 5, it is inherited in an autosomal dominant
pattern, which means parents with mutated gene have a 50% chance of passing the genetic mutation on to each child.
■ Hereditary non-polyposis colorectal cancer(HNPCC), or Lynch
HNPCC (also called Lynch syndrome) is an autosomal dominant manner
that has a high risk of colon cancer as well as other cancers including
endometrial cancer, stomach cancer, urinary tract cancer, and small
intestine cancer. The cause of HNPCC is defective DNA mismatch repair (MMR), which leads to microsatellite instability. MMR is associated with
mutations in genes, including MLH1, MSH2, MSH6, PMS2.
Lynch syndrome is caused by germline mutations in DNA MMR genes.
Finland study found that colonoscopy exams every 3 years was
associated with a reduction in CRC incidence and mortality by 63%.
Recent studies found that risk of CRC was reduced from 10% to 6% after
increasing the frequency of surveillance colonoscopy exams from 3 years to 1-2 years starting at age 20-25 years or 10 years before the youngest
age of CRC diagnosis in the family.
who have fulfilled the following criteria:
(1) CRC diagnosed in a patient who is less than 50 years old
(2) Presence of synchronous (at the same time) or metachronous (at
another time i.e.- a re-occurrence of) CRC or other Lynch syndrome-
associated tumors, regardless of age
(3) CRC with high microsatellite instability histology diagnosed in a
patient less than 60 years old
(4) CRC diagnosed in one or more first-degree relatives with a Lynch
syndrome-associated tumor, with one of the cancers being diagnosed at less than 50 years of age
(5) CRC diagnosed in two or more first-degree or second-degree
relatives with Lynch syndrome-associated tumors, regardless of age
■ Associated hereditary cancer : Colorectal cancer
■ Genes analyzed : 17 genes