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A risk factor is anything that increases a person's chances for developing a disease or condition. Most persons are at average risk of developing colorectal cancer. Common risk factors for colorectal cancer include:

• Age over 50 years
• Male gender
• Diabetes
• Previous radiation to the abdominal area
• High fat diet (especially with high consumption of red meat)
• Tobacco use (it is thought that 12% of colorectal cancer deaths are attributable to smoking)
• Low physical activity
• Moderate alcohol consumption (associated with a two-fold increase in risk)
• African Americans race (the reasons for which are unclear)
• Occupational exposures (i.e., asbestos)

Persons at increased risk for developing colorectal cancer include those with:

• Hereditary colon cancer syndrome
• Personal history of adenomatous polyps or colorectal cancer
• Family history of adenomatous polyps or colorectal cancer
• Chronic inflammatory bowel disease (ulcerative colitis or Crohn's Disease)

Familial Adenomatous Polyposis

Familial adenomatous polyposis (FAP) is a hereditary colon cancer syndrome and accounts for approximately 1% of all cases of colorectal cancer. People with the classic type of familial adenomatous polyposis may begin to develop multiple benign polyps in the colon as early as their teenage years. The number of polyps increases with age and can grow to be hundreds to thousands of polyps. Unless the colon is removed, these polyps will eventually become malignant. The average age at which an individual develops colon cancer in classic familial adenomatous polyposis is about 39 years.

In attenuated familial adenomatous polyposis, the growth of polyps is delayed with an average age of colorectal cancer onset at about 55 years.

A milder type of FAP, called autosomal recessive familial adenomatous polyposis, has also been identified. Persons with this type have fewer polyps than those with the classic type, typically fewer than 100.

Hereditary Nonpolyposis Colorectal Cancer Syndrome

Hereditary nonpolyposis colorectal cancer syndrome (HNPCC), also called "Lynch Syndrome", is an autosomal dominant syndrome accounting for 5-10% of the total colorectal cancer population. Persons with this syndrome develop colorectal carcinoma at an early age (usually 15-20 years earlier than in the general population), although the disease can occur in all age groups.

As its name implies, HNPCC is not associated with the development of polyps (adenomas), however, once formed, adenomas in this population progress to carcinoma more quickly and more often than in the general population (as quickly as 2-3 years). In addition, HNPCC cancers are 6-8 times more common than cancers from FAP.

Typical features of the disease include a family history of colorectal cancer at a relatively young age, a predominance of proximal tumors, and a tendency to have multiple primary tumors (either at the same time or at different times). Certain types of non-colon cancers are also associated with this disease, such as tumors of the endometrium and ovary in women, the stomach, small bowel, liver and gallbladder, pancreas, brain and urological system.

Persons with HNPCC have a greater proportion of mucinous carcinomas and poorly differentiated carcinomas than in the general population.

Criteria for diagnosis (Amsterdam Criteria II) of HNPCC include: