Alternative Names
Colon and rectal cancer; cancer of the colon; colorectal cancer
Symptoms & Characteristics
Colon cancer is cancer of the large intestine (colon), the lower part of the digestive system. Rectal cancer is cancer of the last several inches of the colon closest to the anus. Together, these cancers are often called colorectal cancers.
Symptoms of colorectal cancer may include fatigue, unexplained weight loss, nausea and vomiting; as well as a change in bowel habits such as diarrhea, constipation, blood in stool, and narrow stools.
Treatment
Colorectal cancer treatment may include surgery, radiation, chemotherapy and targeted drug therapies depending on the type and stage of cancer. A colonoscopy may help detect early colorectal cancer.
How Common Is It?
Over 100,000 people are diagnosed with colon cancer each year in the United States, while about 40,000 new cases of rectal cancer are diagnosed.
Genetics & Inheritance
Most cases of colorectal cancer are not inherited and occur sporadically. Cancer is a multifactorial condition, which means it involves a combination of genetic, lifestyle and environmental factors.
- Many risk factors have been proposed to contribute to colorectal cancer risk. Some of these risk factors include a diet low in fiber and high in fat and calories, a history of colon polyps, and smoking cigarettes.
- Studies have established that having ulcerative colitis increases the risk to develop colon cancer. Whether having Crohn's disease also increases colon cancer risk is currently debated.
About 15%-20% of all colorectal cancers are hereditary. Genetic colorectal cancer predisposition can be broken down into different categories including Hereditary Cancer Syndromes and Single Nucleotide Polymorphisms (SNPs).
Hereditary Cancer Syndromes - A hereditary cancer syndrome is caused by an inherited gene mutation that increases the chance to develop one or more types of cancer. Families are more likely to have a hereditary cancer syndrome if there are multiple generations of affected family members with the same cancer (or associated cancers). People who are diagnosed at an unusually young age or have certain rare cancers are also more likely to have a hereditary cancer syndrome. Several different hereditary cancer syndromes have been identified. Click here for more information about Cancer Genetics.
There are a number of hereditary cancer syndromes that confer an elevated risk to develop colorectal cancer. Some of the more common hereditary cancer syndromes associated with colorectal cancer include:
- Lynch syndrome accounts for approximately 1% to 3% of all colon cancers.
Other genes have been associated with susceptibility to colorectal cancer as well.
Single Nucleotide Polymorphisms (SNPs) - SNPs are small variations in a single "letter" of DNA that can be found throughout our entire genetic make-up. Some researchers have proposed that specific SNPs may cause susceptibility to colon cancer in some people. The contributions of these SNPs to colon cancer risk are considered small in comparison to high risk mutations in the hereditary cancer syndromes associated with colorectal cancer. In addition, research is currently often limited to specific ethnic groups. Further research is needed to replicate study findings across different ethnic groups and clearly establish associations.
Genetic Testing
Cancer predisposition testing for the hereditary cancer syndromes associated with colorectal cancer may be available through an in person genetic consultation for people who are considered at risk.
- Not all individuals with colorectal cancer or a family history of colorectal cancer are considered candidates for cancer predisposition testing. Genetic testing options are based on specific criteria and guidelines, which can be discussed with a genetic professional.
- All genetic testing results should be provided and explained in context of the each individual's unique personal and family histories.
- There is considerable debate and concern regarding testing of at-risk individuals younger than age 18 years old for adult-onset conditions (including hereditary cancer syndromes). Such testing is typically unavailable. The American Society of Human Genetics in conjunction with the American College of Medical Genetics as well as the National Society of Genetic Counselors have issued statements regarding this type of testing:
Informational genetic testing for colon cancer susceptibility is available online (over the internet). Go to the Tests tab to link to online providers, compare providers and read provider reviews.
- Some providers offer whole genome scanning, which may include testing for some of the SNPs that have been proposed to influence susceptibility to colon cancer.
- At this point, many genetic professionals do not consider this testing clinically useful or medically relevant, but for informational purposes only.
Colon cancer stool screening is also available online (over the internet). Go to the Tests tab to link to online providers, compare providers and read provider reviews.
- Cancer cells have genetic mutations that occur when a cancer develops. This testing screens for genetic mutations in cancer cells that have shed into stool. This testing does not look for hereditary cancer syndromes and inherited mutations associated with colorectal cancer.
- This testing does not replace colonoscopy and is NOT intended for people with a positive stool blood test (FOBT), a history of rectal bleeding, signs and symptoms that suggest colorectal disease, a personal or family history of colorectal cancer, a personal history of other cancers, or a personal or family history of a known or suspected hereditary cancer syndrome.
The decision to have genetic testing is personal and should always be discussed with trained medical professional.
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