Because colon and rectal cancers arise from the same type of cell and have many similarities, they are often referred to collectively as “colorectal cancer”.
The colon and rectum are part of the digestive system. Together, the colon and rectum make up the large intestine, or large bowel. The colon takes up water and nutrients from food and passes waste to the rectum. The cells lining the colon or rectum can sometimes become abnormal and divide rapidly. These cells can form benign (non-cancerous) tumours or growths called polyps. Although not all polyps will develop into colorectal cancer, colorectal cancer almost always develops from a polyp. Over a period of many years, a polyp’s cells may undergo a series of DNA changes that cause them to become malignant (cancerous).
At first, these cancer cells are contained on the surface of a polyp, but can grow into the wall of the colon or rectum where they can gain access to blood and lymph vessels. Once this happens, the cancer can spread to lymph nodes and other organs, such as the liver or lungs—this process is called metastasis, and tumours found in distant organs are called metastases.