Rectal Cancer (Adenocarcinoma of the Rectum)

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What is Rectal Cancer?

Rectal cancer may be of the adenocarcinoma type and usually arise from the epithelium (the layer of cells) which lines the large intestine. The colon is part of the large bowel. The large bowel starts at the end of the small bowel (the ileum), at the caecum. The caecum has the appendix running off it. The start of the colon is the ascending colon and where this rises to meet the liver (the hepatic flexure) it becomes the transverse colon. The transverse colon goes across the upper abdomen until it becomes adjacent to the spleen (the splenic flexure) and at this point it becomes the descending colon. The large bowel at this point goes down the abdomen to the pelvis at which point it becomes the sigmoid colon (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 it is evacuated through the anus.

Overall, the function of the large bowel is to absorb water from stools. When the ilium enters its contents into the caecum, they are extremely liquid and gradually solidify as the contents progress around the large bowel.

Who gets Rectal Cancer?

Rectal cancer is common but occurs very rarely in young adults. Rectal cancer becomes more common as age increases. People in their 50s, 60s and 70s are most at risk with with sex incidence being slightly more common in females. Geographically, the rectal cancer tumour is found worldwide, but rectal cancer si most common in areas which have low fibre diets. Areas of the world with high fat consumption and low fibre consumption such as Europe, USA and Australia.

Predisposing Factors

There are a number of factors which increase the risk of developing rectal cancer: Hereditary Conditions: At particularly high risk of Rectal cancer are people with hereditary conditions such as Familial Adenomatous Polyposis or Hereditary Non Polyposis Colorectal Cancer. In these conditions, it can occur even in young adults, e.g. late teens and early 20s. Family History of Rectal Cancer: First degree relatives of patients with rectal cancer have an increased risk, particularly if the relative develops rectal cancer at a young age. Polyps: Certain types of polyps, notably villous adenomas have a potential to become malignant. Rectal cancer 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 approximately a ten fold risk of developing the disease and should have a colonoscopy carried out regularly. Diet: A high fat, low fibre diet, especially if high in red meat, is the worst diet that predisposes people to rectal cancer. People who suffer from obesity are also at an increased risk.

Progression

The rectal cancer 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 rectal cancer spread via the blood stream to the liver, which is the most common area of metastasis from this tumour. Other 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 seeding produces small nodules throughout the abdomen which irritates tissues and causes the production of large amounts of ascites (fluid). Direct spread from the rectum may attach the tumour to the bladder in males and cause fistulas. In females it may invade the vagina or adjacent pelvic organs.

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