APC gene testing and cancer
APC gene testing is a genetic screening performed to diagnose familial adenomatous polyposis (FAP), a hereditary condition characterized by the development of precancerous polyps in the colon. These adenomatous polyps are initially benign, but if left untreated, they can progress to colorectal cancer. The testing involves sequencing the DNA of individuals showing symptoms of FAP to confirm the diagnosis and to identify specific mutations in the APC gene. Genetic testing is also recommended for family members of affected individuals to assess their risk and determine if preventive measures are necessary.
Before testing, patients may meet with a genetic counselor to understand the implications of potential test results, which can be positive, negative, or inconclusive. The procedure requires a blood sample, which is analyzed in a laboratory to identify any mutations linked to FAP. The results can have significant psychological effects, making genetic counseling an important part of the process. If a mutation is detected, close relatives can be screened to assess their risk, as those with a first-degree relative with colorectal cancer face a higher lifetime risk of developing the disease. Prophylactic treatments, including surgical removal of polyps, may be advised for individuals with identified cancer-causing mutations in the APC gene.
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APC gene testing and cancer
Also known as: Adenomatosis polyposis coli gene testing
Definition:The APC gene is a tumor-suppressor gene that is often mutated in colorectal and other cancers. Most mutations leading to colorectal cancer occur spontaneously in the digestive tracts of affected individuals, but approximately 1 percent of cases result from inherited mutations in APC, as noted by the American Society of Clinical Oncology in 2013. Testing for mutations in APC usually involves determining the deoxyribonucleic acid (DNA) sequence of a patient’s APC gene, but other screens are sometimes used.
Cancers diagnosed: Familial adenomatous polyposis, familial colon cancer
Why performed:APC gene testing is performed to diagnose familial adenomatous polyposis (FAP), an inherited condition in which precancerous polyps form in the colon. Although these polyps are initially benign, they may develop into cancer if untreated. The DNA of patients exhibiting symptoms of FAP is sequenced to confirm diagnosis and to characterize the mutation in APC. Because FAP is an inherited disorder, genetic testing is often done in relatives of those afflicted with FAP in order to determine whether prophylactic treatment is required.
Patient preparation: Patients considering genetic testing may meet with a genetic counselor to discuss the benefits and risks of the test and the significance of negative, positive, and inconclusive tests. The material required for genetic testing is obtained from a blood sample.
Steps of the procedure: Blood samples are sent to a clinical laboratory that offers APC screening. DNA is purified from the blood sample, and the DNA that encodes for APC is amplified by polymerase chain reaction (PCR) and sequenced using standard, automated methods.
After the procedure: The patient may consult with a physician or genetic counselor to discuss the implications of the test results.
Risks: Complications from drawing blood are rare but may include pain, bleeding, hematoma, or infection. Because the information obtained from APC screening may have dramatic psychological effects, it is essential that patients be offered genetic counseling.
Results: Sequence analysis allows clinicians to identify the specific DNA mutation(s) present in a FAP patient. Once the mutation has been identified, close relatives can be screened to determine if they share the FAP-causing mutation. According to the National Cancer Institute (2014), for individuals who have a first-degree relative with colorectal cancer, the absolute risk of developing it themselves by age seventy-nine is 9 percent as compared to 4 percent for those with no family history. Surgical polyp removal and other prophylactic treatment may be recommended for individuals who carry cancer-causing mutations in the APC gene.
Bibliography
"APC." Genetics Home Reference. US National Library of Medicine, Mar. 2013. Web. 18 July 2014.
Chan, Andrew T., and Daniel C. Chung. "Hereditary Colon Cancer: Colonic Polyposis Syndromes." Principles of Clinical Cancer Genetics. Ed. Daniel C. Chung and Daniel A. Haber. New York: Springer, 2010. 63–76. Print.
"Familial Adenomatous Polyposis." Cancer.net. Amer. Soc. of Clinical Oncology, May 2013. Web. 18 July 2014.
"Genetics of Colorectal Cancer." Cancer.gov. Natl. Cancer Inst., Natl. Inst. of Health, 11 July 2014. Web. 21 Aug. 2014.
"Genetics Testing for Hereditary Cancer Syndromes." Cancer.gov. Natl. Cancer Inst., Natl. Inst. of Health, 11 Apr. 2013. Web. 21 Aug. 2014.
Rodriguez-Bigas, Miguel A., et al. Hereditary Colorectal Cancer. New York: Springer, 2010. Print.