Colon cancer is the second most common type of cancer. Although it may not have attracted as much media attention as other cancers, the medical community is making efforts to better understand its causes and to discover possible cures, and their efforts have paid off in the form of new treatment options and screening methods.
Cancer develops when regular cells produce mutations during cell division that cause those cells to grow and survive much longer than healthy cells. These “immortal” cells divide into more cells, potentially leading to the development of a malignant tumor.
Anyone can develop colon cancer in their lifetime, but there are certain factors that can put someone at a higher risk of obtaining this often deadly condition.
-- Age: Individuals who are 50 years or older are more at risk than those younger. However, colon cancer has been detected in patients as young as 22.
-- Family history: If a close relative has been affected by colon cancer, other family members should undergo regular screening. A genetic predisposition for developing colon cancer does exist, and genetic screening is also an option.
-- Medical history: patients who have previously been treated for cancer of the colon, rectum, ovary, endometrium, or breast tend to be more at risk for developing colon cancer.
“A history of polyps and inflammatory bowel disease is associated with a higher risk,” explained Dr. Louis Liu from the University Health Network in Toronto. “It has also been indicated that there may be some association of smoking and possibly obesity with a higher risk of colon cancer.”
Efforts have been made to try and develop preventative measures for colon cancer, but none are conclusive at this time. As polyp formation is considered to put a patient at higher risk of colon cancer, the finding that the medications Vioxx and Celebrex seemed to prevent polyp formation in animal studies looked promising.
Dr. Steve Gallinger at Mount Sinai Hospital in Toronto, noted that this treatment avenue hit a roadblock when Vioxx was pulled from the market.
"Celebrex was still hoped to prevent colon polyp formation, but when large studies were done on humans, an excess number of cardiac events (heart attack and stroke) were experienced by the patients taking Celebrex compared to patients on a placebo," Dr. Gallinger added.
Researchers are now looking for ways to develop similar drugs that have the same polyp-reducing benefits, without the side effects.
Primary preventative measures could still be promising and also include a proper and healthy diet high in certain compounds.
“Currently, dietary agents such as vitamin D and calcium are being studied and may be a good alternative to preventative drugs," said Dr. Gallinger.
However, these studies are incomplete, and information regarding dosage levels and the magnitude of effect of these supplements is uncertain.
"The golden standard in secondary prevention is still considered colonoscopy," Dr. Gallinger explained.
A colonoscopy takes about 30 to 60 minutes during which the doctor uses a colonoscope, a long flexible instrument that is about one half inch in diameter, to visually search the lining of the colon for abnormalities. The colonoscope is inserted through the rectum and maneuvered to the upper end of the large intestine. If during the procedure the doctor detects some abnormal tissue, a small sample may be removed for biopsy.
While everyone should start screening at the age of 50, those patients who have a strong family history should screen starting at the age of 40, or 10 years earlier than the age of the family member at diagnosis. Patients who are weary of the traditional colonoscopy can consider a "virtual colonoscopy", in which a CT (computed tomography) scan creates a three-dimensional image of the colon in a non-invasive manner.
However, the virtual colonoscopy still requires the same preparation as a regular colonoscopy (fasting, clear bowels) and has not yet replaced it. Other tests mentioned by Dr. Liu include fecal occult blood tests and x-rays using barium enemas. Although Dr. Liu does not recommend any one test over another, he said a colonoscopy should be performed if the barium enema shows potential polyps.
One percent of patients with colon cancer have a mutation in a gene called MYH. Although this genetic susceptibility for colon cancer is rare, it does suggest genetic screens can be useful if there is a family history.
However, some patients may have the mutation and develop cancer without any prior history in the family. The reason no other relatives are affected is because the mutation is linked to cancer recessively, thus in order for an individual to develop colon cancer, he or she needs to have two copies of the “defective” gene, one from each parent. If this is the case, genetic screening could be useful for siblings.
"Patients who carry the mutation are, however, predisposed to many polyps," said Dr. Gallinger.
If a routine screening shows that many polyps are present, it could be a hint that there is a mutation in the MYH gene, causing MYH Associated Polyposis (MAP).
Over the past decade, the medical community has been able to celebrate many advances in the detection and cure of colon cancer. There are currently six to seven approved drugs for the treatment of colon cancer, compared to only one 10 years ago. This has resulted in a dramatically increased life span for patients with metastatic colon cancer.
Currently, many pharmacogenetic studies are being conducted to understand why certain patients respond better to certain drugs. This can help the medical community better predict which treatment option is best suited for each individual patient.
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