When cells in the colon or rectum mutate and begin to grow uncontrollably, this can form a malignant tumour, known as cancer. This tumour can grow into nearby tissue, as well as spread (metastasize) to other areas of the body. This will lead to a diagnosis of colorectal or bowel cancer.
The intestine, made up of the small and large intestine, is a key part of the digestive system. The colon and rectum are parts of the large intestine, and are about 2 metres long. The main functions of the intestine are to absorb nutrients and water from food, and to eliminate waste. The large intestine is often referred to as the bowel, so colon cancer and bowel cancer are the same condition.
The most common type of colorectal cancer is adenocarcinoma, which starts in cells that make mucus along the inner lining of the colon or rectum (called the mucosa). Mucus helps stool (feces) move through the colon and rectum.
Rare subtypes of adenocarcinoma, such as mucinous adenocarcinoma and signet ring cell carcinoma, are named based on how they look under a microscope.
There are also quite a few rare forms of cancerous colorectal tumours:
- Squamous cell carcinoma, which is treated as anal cancer.
- Neuroendocrine tumour (NET).
- Soft tissue sarcoma.
- Gastrointestinal stromal tumour (GIST).
- Non-Hodgkin lymphoma, such as MALT lymphoma.
Information taken from the Canadian Cancer Society.