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Colorectal Cancer: Causes and Risk Factors

Colorectal cancer (CRC) is usually caused by a complex combination of factors rather than one single element. Several of these factors, however, appear to increase the likelihood of developing the disease.

Research suggests that most cases of CRC begin as adenomatous polyps. If the polyps are detected early, during screening, the condition can be treated before it becomes cancerous.

Some people develop colorectal cancer without being affected by any of the more typical risk factors.

Heredity and Genetics

Heredity and genetic predisposition are major identifiers. Research has shown that a family history of colorectal cancer in parents, brothers, sisters or children, especially where the person developed cancer before the age of 45, presents a high risk factor.

If you have a personal or family history of any of the following conditions, then you may have an increased likelihood of developing CRC:

Previous CRC or other cancers, e.g. breast, uterus, or ovarian cancer
Adenomatous polyps, the small growths on the inner wall of the colon and rectum; in most cases, the colon polyp is benign (harmless)
Inflammatory bowel disease, such as Crohn's disease or ulcerative colitis
Diabetes, often in combination with obesity
Zollinger-Ellison Syndrome, the rare digestive disorder caused by tumors in the pancreas or duodenum that leads to ulcers in the stomach and duodenum
Cytomegalovirus (CMV), a virus that may affect people with weakened immune systems
Gardner's syndrome, which may result in development of colon polyps and colorectal cancer at a young age. Gardner's syndrome may also cause non-cancerous tumors to develop.

Inflammatory Bowel Disease
CRC may be a complication of inflammatory bowel diseases (IBD), such as Crohn's disease and ulcerative colitis. While research has not been able to establish how much of a risk IBD is, what has been established is that the more severe the IBD and the longer the duration of the disease, the more likely the development of CRC. More information on both of these diseases can be found at Crohn's Disease and Ulcerative Colitis Information.

Familial Adenomatous Polyposis (FAP)

Familial adenomatous polyposis is an inherited disorder of the colon and rectum that significantly increases a person's risk of developing colorectal cancer. The offspring of an affected parent have a fifty percent increased chance of inheriting the specific gene that causes the problem.

Typically, people who suffer from FAP develop hundreds of polyps in the colon and rectum. Without early detection and preventive surgery, cancer is highly likely to develop in one or more of the polyps.

With the FAP condition, abnormal cells tend to grow slowly, over several years and "clump" eventually into pre-cancerous adenomas. Cancer caused by FAP is most likely to occur between the ages of thirty and fifty. By the time an adenoma becomes cancerous, it may have grown as large as four to five centimeters in diameter.

A New Risk Factor

Findings from two recent studies conducted by the Howard Hughes Medical Institute suggest that carriers of the rare Bloom syndrome gene (BLM) have an increased likelihood of developing colorectal cancer. Although Bloom syndrome occurs in all ethnic populations, it is far more prevalent among the Jewish people of European descent known as Ashkenazi Jews.

Those Ashkenazi Jews with the genetic mutation are twice as likely to develop colon cancer as the rest of the US population.

Referring to these findings, Joanna Groden of the HHMI points out that "knowing your family history of disease is very important." She continues, "Even cancers that we think of as common and age-related can have a hereditary component".

More Risk Factors

Besides Bloom syndrome, the following factors have been identified as predictive of CRC:

Age: If you are aged fifty or older and have no other risk factors, your likelihood of developing CRC is considered to be average.
Diet: A diet high in saturated (animal) fats increases the odds; a low fat diet, rich in fresh fruit and vegetables reduces them.
Physical inactivity: Lack of exercise and a sedentary lifestyle appear to increase the danger of CRC.
Obesity: A link has been identified between obesity and an increased risk of developing CRC. Excess fat around the waist, in particular, has been linked with a change in metabolism that encourages cell growth in the colon and rectum.
Smoking: Eliminating the use of tobacco is known to reduce the likelihood of developing CRC.
Heavy alcohol consumption: Studies have established a link between a combination of alcohol and tobacco with an increased risk for colorectal cancer.

The Obesity Factor
Current research is looking at the links among obesity, diet and the risk of developing colorectal cancer. Although studies have shown that a diet high in fresh vegetables, fruit and fiber and low in animal fats is likely to reduce risk, further research is required to explain exactly what role these factors play.

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