Where is the colon and rectum?

The colon and rectum together forms the large intestine. It is the last part of the digestive system. It begins where the small intestine ends at the right lower corner of the abdomen. It travels upwards towards the liver at the right upper quadrant, then turns and goes across the abdomen to the left upper quadrant. From there, it turns downwards and travels to the left lower part of the abdomen.

It then travels towards the centre of the pelvis and goes straight down and ends at the anus. The rectum forms the last 15cm of the large intestines and lies within the pelvis. It is so named because it is relatively straight.

What is Cancer?

Cancer is an abnormal growth of cells that has the ability to invade into surrounding organs as well as spread to distant sites.

How does Colorectal Cancer forms?

Colon and rectal cancer originates from the inner lining or mucosa of the colon and rectum. The lining of the colon is continuously growing and shedding. As such, the lining or mucosa is undergoing cell replication all the times. With each replication, there is always a chance of a mutation. Although most mutations are recognised as an error by the body and the mutant cell is removed, sometimes these mutant cells escape the body defence mechanism and continue to grow. As they grow, more mutation may occur and after a sequence of 4 or 5 mutations in the cell, they may turn cancerous.

Most of the colon cancer follows the adenoma-carcinoma sequence. What this means is that the colon wall first mutates into adenoma (a non-cancerous form) and over time with more mutation, changes into carcinoma (cancer).

The adenoma is usually in the form of a polyp which is a fleshy protuberance from the colon wall. Larger polyps may appear to have a stalk due to the weight of the polyp pulling on the colon lining.

With time, the adenoma type tissue in the polyp will turn cancerous. It then invades back into the polyp and up the stalk (if there is one) and eventually into the wall of the colon.

Once the cancer has invaded into the wall, it can then spread to distant organs either via the blood stream or the lymphatic system.

• Colorectal Cancer
• Symptoms and Signs of Colon and Rectum Cancer
• Who is At Risk?
• Investigations
• Treatment
• Other Treatment Options
• Staging of Colon and Rectum Cancer
• Follow up