Colon Cancer (Adenocarcinoma of the Colon)

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What is Colon Cancer?

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Colon cancer may be of the adenocarcinoma type and usually arises from the epithelium (layer of cells) lining the inside of the large intestine. The colon is part of the large bowel. The large bowel starts at the lower end of the small bowel (the ileum), at the caecum. The appendix runs off the caecum. The start of the colon is the ascending colon, which becomes the transverse colon where it meets the liver (the hepatic flexure). The transverse colon goes across the upper abdomen until it is adjacent to the spleen (the splenic flexure), where it becomes the descending colon. At this point, the large bowel goes down the abdomen to the pelvis, where it becomes the sigmoid colon (named because it curves in an "S" shape, sigma being the Greek for "S"). The sigmoid colon terminates at the rectum, which acts as a storage pouch for faeces before they are evacuated through the anus.

Overall, the function of the colon (large bowel) is to absorb water from the stool. When the ilium deposits its contents into the caecum, they are extremely liquid. They gradually solidify as they progress around the large bowel.

Who gets Colon Cancer?

Colon cancer is common but occurs very rarely in young adults. It becomes more common with age. Females more than 50 years old are most at risk. Geographically, the tumour is found worldwide, but is most common in areas that have low fibre diets. Areas of the world with high fat consumption and low fibre consumption include Europe, the US and Australia.

Predisposing Factors

Hereditary: At particularly high risk are people with hereditary conditions such as familial adenomatous polyposis or hereditary non polyposis colorectal cancer. With these conditions, colon cancer can occur even in patients in their late teens and early twenties. Family History: First degree relatives of patients with colorectal cancer have an increased risk of colon cancer, particularly if the relative develops it at a young age. Colon Polyps: Certain types of polyps, notably villous adenomas have the potential to become malignant. Patients who have previously had a polyp in the large bowel should undergo regular colonoscopy (ask your doctor how often). Inflammatory Bowel Disease: Patients who suffer from ulcerative colitis have a ten-fold risk of colon cancer, and should undergo regular colonoscopy. Diet: A high fat, low fibre diet, especially if high in red meat, is linked to colon cancer. People who suffer from obesity are also at an increased risk.

Progression

The tumour spreads by invading the bowel wall. Once it crosses through the muscle layer within the bowel wall, it enters the lymphatic vessels, spreading to local and then regional lymph nodes. Sometimes it spreads via the blood stream to the liver, which is the most common area of metastasis from this tumour. Other human organs that may be affected by blood-borne spread are the lungs, less often the bones, and even less often the brain. If a lot of tumour cells get through the bowel wall, they tend to float around as a small amount of fluid within the abdomen and can seed the covering of the bowel (peritoneum). This type of cancer seeding produces small nodules throughout the abdomen that irritate tissues and cause the production of large amounts of ascites (fluid).

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