What is colon cancer?
Colon cancer is a malignant growth in the colon. It usually affects the rectum as well so the joint term is coloretal cancer (CRC). The colon is the longest part of the large intestine and processes all the waste material in the bowels that are eventually passed into the rectum and evacuated as faeces. Like the rest of the gut, it is lined with epithelium known as the mucosa. Most colorectal cancers starts as overgrowths of mucosal tissue know as polyps or adenomas. Not every polyp is cancerous though. Colorectal cancer is among the five most common types of cancers and screening in high risk individuals is advisable.
Causes and Risk factors
The exact cause of colorectal cancer is unclear but it appears that mutations in certain genes are largely responsible. This allows for uncontrolled growth of tissue either by failure of the regulatory mechanisms to monitor abnormal patterns of growth or trigger excessive cell growth. Some of these genes, known as oncogenes, when mutated can increase the risk of colon cancer yet not cause it. Successive generations may therefore also be at the risk.
Other causes and significant risk factors may include :
- Age. Most patients diagnosed with colorectal cancer are over 50 years of age and the risk increases with advancing age.
- Preexisting colorectal polys are more common after the age of 50 years but most cases are benign (non-cancerous).
- Family history of colorectal cancer is considered as a very important risk factor when a first-degree relative (parent, sibling, child) has been diagnosed with CRC.
- Personal history of colorectal cancer is another significant risk factor as the chance of recurrence is great.
- Hereditary nonpolyposis colon cancer (HNPCC) is the most common cause of inherited CRC. It causes about 2% of colorectal cancer cases.
- Familial adenomatous polyposis (FAP) causes about 1% of CRC cases. It is a rare inherited condition in which multiple polyps are formed in colon and rectum.
- Inflammatory conditions of colon like ulcerative colitis and Crohn’s disease (inflammatory bowel disease).
- Diet that is low in fibre, particularly with limited fruits and vegetables, and high in fat increases the risk of colorectal cancer.
- Smoking increases the risk of all types of cancers.
- Excessive alcohol consumption may also be a risk factor in colorectal cancer.
Signs and Symptoms
Generally the symptoms of colorectal cancer develop very late and are similar to other gastrointestinal diseases which can be misleading. The most common symptoms of colorectal cancer is a change in bowel habit with constipation alternating with loose stools (some patients may describe it as diarrhoea). Colorectal cancer patients also describe a sensation of incomplete emptying of the bowels even after passing stools. Other symptoms like blood in the stool, severe abdominal pain and unexplained weight loss that may accompany the change in bowel habit should raise the concern about colon cancer and warrant further investigation. Nausea, vomiting and malaise may develop with time.