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CancerQuest > Introduction to Patient Information > Introduction to Cancer by Type > Colon and Rectal Cancer: Introduction > Colon and Rectal Cancer: Risk Factors

Colon and Rectal Cancer: Risk Factors

Factors that may influence risk of developing colorectal cancer include⁽¹⁾:

• Family History of Colorectal Cancer
• Age
• Diets rich in red or processed meat
• Excessive drinking of alcohol
• Obesity
• Smoking

The relative effects of these and other risk factors in any given case of cancer is variable and very difficult to determine with accuracy at this time. Some of these and other risk factors are discussed on the following pages.

Watch a clip about colon cancer prevention and then click here to watch the full interview with Dr. Roberd Bostick.

Family History of Colorectal Cancer
Cancer cases can be grouped into two broad categories, sporadic and familial. Sporadic cancers are those in which the affected individual does not have a known family history of the disease. Familial cancers tend to occur in several generations of a family and affected individuals often have close relatives (brother, sister, father) with the same cancer type. It is possible that these individuals inherit defective genes that lead to the development of a particular cancer type. Individuals with a family history of colorectal cancer are at an increased risk of developing the disease. The degree of risk depends upon the type of relative affected. For example, risk is higher if an immediate family member has been diagnosed with colorectal cancer. The more closely related an individual is to someone with colorectal cancer, the more likely they will share the defective genes. Inherited colorectal cancer accounts for about 5% of all colorectal cancer cases.⁽²⁾

The two major colorectal cancer susceptibility syndromes are called familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC):

Familial adenomatous polyposis (FAP): An abnormal growth in the lining of the colon or rectum is called a polyp. Common types of polyps include adenomatous polyps (adenomas), hyperplastic polyps, and inflammatory polyps. Hyperplastic and inflammatory polyps generally do not pose problems. Adenomatous polyps, however, can progress into cancer.⁽³⁾

FAP is a syndrome caused by mutation of the APC (adenomatous polyposis coli) gene. Individuals who are born with this mutation develop hundreds to thousands of adenomatous polyps along their colon and rectum. If left untreated, one or more of these polyps is very likely to progress into cancer.⁽³⁾ The average age of cancer onset in these individulas is 40.⁽⁴⁾ It is possible to detect and remove adenomatous polyps during screening.

The APC gene will be discussed in the Colorectal Cancer Tumor Biology pages of this section

Familial adenomatous polyposis: the mucosal surface of the colon is carpeted with numerous early adenomas. (Image courtesy of: C. Whitaker Sewell, MD - Professor of Pathology, Emory University School of Medicine)

Hereditary non-polyposis colorectal cancer (HNPCC): HNPCC, also called Lynch syndrome, is a syndrome caused by mutation of genes that encode proteins involved in DNA repair, in particular the MLH1 and MSH2 genes.⁽⁵⁾ Characteristics of HNPCC include development on cancer by the average age of 45, cancer located in the proximal colon, and increased risk of developing certain cancers located outside the colon.⁽⁶⁾ HNPCC is not associated with the presence of polyps in the colon or rectum.

The MLH1 and MSH2 mismatch repair genes will be discussed in the Colorectal Cancer Tumor Biology pages of this section

Age

For almost all types of cancer studied to date, it seems as if the transition from a normal, healthy cell to a cancer cell is step-wise progression that requires genetic changes in several different oncogenes and tumor suppressors. This is one reason why cancer is much more prevalent in older individuals. In order to generate a cancer cell, a series of mutations must occur in the same cell. Since the likelihood of any gene becoming mutated is very low, it stands to reason that the chance of several different mutations occuring in the same cell is truly very unlikely. For this reason, the cells in a 70 year old body have had more time to accumulate the changes needed to form cancer cells but those in a child are much less likely to have acquired the required changes. Of course, some children do get cancer but it is much more common in older individuals. More than 91% of patients are diagnosed with colorectal cancer over the age of 50.⁽¹⁾ The graph below shows colon cancer rates in the United States as a function of age. The graph was obtained from the National Cancer Institute. ⁽⁷⁾

Dietary Factors

Incidence of colon cancer correlates greatly with certain lifestyle factors, including diet. It is very difficult, however, to identify dietary items that cause a particular cancer. Studies show correlations between chronic heavy alcohol consumption and low folate intake and an increased risk of colorectal cancer.⁽⁸⁾ On the other hand, some dietary factors are associated with a decreased risk of colorectal cancer. Research suggests that a diet rich in fruits and vegetables may provide a protective effect against the disease.⁽⁹⁾Calcium is also thought to possibly play a protective role. Studies with labratory animals show that calcium may bind to fatty acids and bile and decrease their harmful effect on the cells that make up the lining of the colon.⁽¹⁰⁾ The influence of these dietary factors on colorectal cancer risk is a topic still under debate.

Obesity

Several studies have found an association between increasing body mass index (BMI) and risk of colorectal cancer. The association has been found more consistently in men than in women, however. This difference may be caused by the effect of the female hormone estrogen, which is thought to have a protective effect against colorectal cancer. Women with high body mass indexes tend to have higher estrogen levels compared to women with lower body mass indexes. The higher estrogen levels may counteract the negative effects of an elevated BMI.⁽¹¹⁾

Smoking

Studies have found an association between tobacco use and an increased number of hyperplastic polyps in the colon and rectum. While most do not, hyperplastic polyps may sometimes develop into colorectal cancer. The link between tobacco and hyperplastic polyps appears to be more dependent upon how recently the smoking occurred rather than duration of smoking.⁽¹²⁾

References for this page:

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