What is colorectal cancer?

Symptoms of colorectal cancer

Risk factors for developing colorectal cancer

Risk factors for developing colorectal cancer

There are numerous dietary, environmental, and hereditary factors that can increase one’s risk for the development of colorectal cancer. In the absence of any symptoms, the following factors play an important role in determining one’s risk for colorectal cancer and the need for any evaluation such as colonoscopy:

1. Previous history of colorectal polyps or cancer

All patients who have previously been diagnosed with colorectal polyps are at a significantly higher risk for subsequent development of colon or rectal polyps. Similarly, patients who have previously been diagnosed with colorectal cancer and have not had their entire colon and rectum removed by surgery are at increased risk for subsequent development of colorectal polyps and cancer. For this reason, it is often recommended that a "routine" follow-up colonoscopy be performed in all individuals who have had previously resected polyps or cancer in the past.

2. Strong family history of colorectal cancer

Most colorectal cancer occurs sporadically in an individual without any previous family history of polyps or cancer. In about one third of all cases, however, there is a family history of colon cancer and the risk of an individual developing colorectal cancer depends on whether a known hereditary cancer syndrome exists in that family or not. The known genetically-defined hereditary syndromes include:

· Familial adenomatous polyposis (FAP) or adenomatous polyposis coli (APC)

This disease is due to an inherited defect in the recently identified APC gene and accounts for less than 1% of all colorectal cancers. Parents with this syndrome have a 50% chance of passing the defective gene to their offspring. If their children have inherited the defective gene, the disease will develop in all cases and is characterized by the development of hundreds to thousands of small polyps in the colon. In such individuals, there is 100% chance of eventually progressing on to develop colon cancer, often before age 40. Such individuals often undergo resection of their colon at a young age to prevent colon cancer.

· Gardner’s syndrome [link]

This syndrome is also due to an inherited defect in the APC gene and presents with identical colonic disease as in FAP. In addition, patients may develop abnormalities of the skin, teeth, and bones and may develop benign fibrotic tumors in their abdomen called desmoid tumors.

· Hereditary non-polyposis colorectal cancer (HNPCC) syndrome [link]

This disease is due to an inherited defect in one of 4 different genes that are involved in repairing damage to DNA, the genetic material of the cell. HNPCC may account for up to 10% of all colorectal cancers diagnosed today. Children also have a 50% chance of inheriting the defective gene from an affected parent and developing the disease themselves. If they inherit the defective gene and develop the disease, it is characterized by the development of only small numbers polyps in the colon. Like FAP, however, there is also a high likelihood of progressing on to develop colon cancer at a young age. In addition to developing colon cancer, some families with this syndrome may be at increased risk for development of tumors elsewhere in the gastrointestinal tract, uterus, ovaries and urinary tract.

The majority of patients with a personal family history of colorectal cancer do not fit into one of these inherited syndromes mentioned above where the risk of developing colorectal cancer is very high. Nonetheless, having a single first-degree relative (i.e. a mother, father, brother, sister, or child) with colon cancer significantly increases one’s own risk for this disease. The magnitude of this risk depends on:

1. The number of relatives affected (greater risk with higher numbers of affected family members)

2. The age of their initial diagnosis (greater risk with lower age of initial diagnosis in a family member).

Patients with a strong family history defined as 1 or more first-degree relatives with colorectal cancer should seek consultation with their physician for further recommendations.

3. Chronic inflammatory bowel disease or ulcerative colitis

Patient with longstanding (i.e. greater than 10 years) inflammatory bowel disease or ulcerative colitis, particularly those with involvement of the entire colon and rectum are at slightly higher risk for subsequent development of colorectal cancer. Some gastroenterologists recommend periodic screening of such individuals with full colonoscopy, although the frequency and interval of such examinations has not been agreed upon fully.

4. Diet

One of the most striking features about colorectal cancer is the vast differences in incidence rates or numbers of newly diagnosed cases in different parts of the world. In less-developed regions such as parts of Africa, Asia and Central and South America, colorectal cancer is very rare compared to developed countries such as the United States and Europe, where the incidence may be ten-fold greater. Much of this difference has been attributed to differences in diet. Diets that are low in fiber and high in fat and meat content typically confer a high risk for colon cancer. Thus, a diet high in fiber and low in fat is believed to be protective.

In studies of immigrant populations who move from low-risk regions to high-risk regions, the deleterious effects of environmental and dietary factors have been shown to increase the risk within as brief a period of time as 15-20 years. In addition to a high fiber. low fat diet, higher consumption levels for certain vitamins and minerals, including calcium, vitamin D, vitamin E, and selenium, have also been shown to have modest protective effects against the development of colorectal cancer.

5. Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDS)

Several studies now strongly suggest that long-term and regular ingestion of small doses of aspirin can substantially reduce the risk for development of colorectal cancer. Similar results have been shown for regular use of other arthritis and pain medications such as sulindac, piroxican and others, collectively known as non-steroidal anti-inflammatory drugs (NSAIDs). Acetominophen, the pain reliever in Tylenol and other over-the-counter, non-aspirin products, has not been shown to be protective against colorectal cancer. A recommendation for the regular use of aspirin and NSAIDs for the prevention of colorectal cancer has not been forthcoming due to the serious side-effects of these medications which frequently include gastrointestinal bleeding and occasionally, toxicity to the kidneys. Active research is currently underway to develop similar medications which reduce the incidence of colon and rectal cancer and polyps and yet possess minimal toxicity and side-effects.

6. Activity level

Epidemiologic studies have shown a slightly increased risk for development of colorectal cancer in obese and sedentary individuals compared to active and non-obese subjects. The reason for this is unclear but may involve dietary differences between the two groups.

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