What is colon cancer?
This article was last reviewed and updated on September 10, 2018.
by Jason Wasserman, MD PhD FRCPC
The colon is a part of the gastrointestinal tract which also includes the mouth, esophagus, stomach, small bowel and anus. The colon is a long hollow tube that starts at the small bowel and ends at the anal canal. The functions of the colon are to absorb water from the food that we eat and to move waste out of the body.
The inner surface of the colon is lined by epithelial cells that form structures called glands. The tissue that surrounds and supports the glands is called the lamina propria. Together, the glands and the lamina propria form an area called the mucosa. Below the mucosa is the wall of the colon which is made up of three layers: a thin supportive tissue (the submucosa), a thick bundle of muscles (the muscularis propria), and a layer of fat (the subserosal adipose tissue). The outer surface of the colon is lined by a very thin layer of tissue called serosa.
Cancer is a word used to describe a disease made up of abnormal cells that have the ability to increase in number faster than normal cells, damage or destroy surrounding normal tissue, and travel (metastasize) to other parts of the body. Most colon cancers grow as a large group of cells called a tumour. Pathologists call a tumour in the colon made up of cancer cells a malignant tumour or a malignancy. Another word for a tumour is neoplasia.
Colon cancer is a general term that is used to describe any type of cancer that starts from cells normally found in the colon. However, there are several different types of colon cancer and the prognosis and treatment will depend on the specific type of colon cancer seen by your pathologist. Most colon cancers develop from the cells that line the glands.
Types of colon cancer
The most common type of colon cancer is called adenocarcinoma. This type of tumour accounts for approximately 80% of all colon cancers and it is one of the most common cancers among adult men and women around the world.
Often, adenocarcinoma starts in a small area of abnormal tissue called an adenoma. For this reason, adenomas in the colon are called a precursor disease because while they are themselves not a cancer, they can turn into cancer over time. Common types of adenomas in the colon include tubular adenomas, tubulovillous adenomas, villous adenomas, and sessile serrated adenomas. You can reduce your risk of developing cancer in the colon by having any adenomas removed in a procedure called a colonoscopy.
Other less common types of colon cancer include mucinous adenocarcinoma, medullary carcinoma, neuroendocrine carcinoma, and lymphoma.
Most colon cancers are first diagnosed after a procedure called a biopsy is performed to remove a small sample of tissue the area of the colon that your doctor identified as abnormal. The piece of tissue is then sent to a pathologist who examines it under the microscope. If cancer is seen in the tissue, your pathologist will then determine the specific type of cancer. The type of cancer is very important because your doctors will use this information to decide what type of treatment is best for you.
Your pathology report after surgery
Most patients diagnosed with colon cancer are offered surgery to remove the tumour. Some patients will also be offered radiation therapy or chemotherapy before or after the surgery is performed. If you have surgery to remove the tumour from your body, the entire tumour will be sent to a pathologist for examination. In addition to the tumour, other tissues may also be removed and sent to pathology although the amount of additional tissue removed will depend on your diagnosis.
After the tumour is removed, your pathologist will determine the size of the tumour and where the tumour cells are located within the colon. Your pathologist will also closely examine the cut edges of the tissue (the margins) to make sure that no tumour cells were left inside your body. Other important prognostic factors such as the presence of tumour cells around a nerve (perineural invasion) or inside blood vessels or lymphatics (lymphovascular invasion).
If you received treatment (either chemotherapy or radiation therapy) prior to your surgery, your pathologist will also determine how well the treatment worked by looking at how much of the tumour is still alive (viable). Finally, your pathologist will carefully examine any lymph nodes removed at the same time as the tumour to see if any of them contain cancer cells (lymph node metastases). All of these details will be in your final pathology report.