colorectal cancer
Meaning of colorectal cancer: Because a polyp usually takes years to turn malignant, this is one of the few cancers screening can prevent rather than merely find early.
Definition of colorectal cancer
Colorectal cancer is cancer of the colon, the rectum, or both, the final stretch of the large intestine that absorbs water and holds waste before it is passed. Almost all cases are adenocarcinomas, arising from the gland-forming cells of the bowel lining. Most begin as a polyp, a small growth on that lining that is not cancer when it first appears.
How does it develop?
The usual sequence starts with a polyp. Two kinds matter: adenomas, and sessile serrated lesions, which are flatter and harder to see. Both are benign at the outset. Over years a minority accumulate genetic changes that let their cells ignore the normal limits on growth, invade through the bowel wall, and eventually reach lymph nodes or the liver. Hyperplastic polyps, the other common finding, do not follow that path. Because the interval between a polyp forming and a cancer emerging is measured in years, removing the polyp interrupts the process before there is anything to treat.
What symptoms can it cause?
Often none, particularly early and particularly on the right side of the colon, where the bowel is wide and stool is still liquid. When symptoms do appear they include a lasting change in bowel habit, blood in the stool that may be bright red or dark and tarry, narrowed stools, a feeling that the bowel has not fully emptied, cramping abdominal discomfort, unexplained weight loss, and fatigue from slow blood loss producing iron deficiency. None of these is specific, and all occur far more often with benign conditions.
How is it looked for?
| Approach | What it involves |
|---|---|
| Colonoscopy | Direct view of the whole colon; polyps can be removed during the same procedure |
| Stool tests | Detect hidden blood, or blood plus altered DNA shed by a tumor; a positive result leads to colonoscopy |
| CT colonography | Imaging that reconstructs the bowel; findings still need colonoscopy to act on |
| Flexible sigmoidoscopy | Examines the rectum and lower colon only |
Only colonoscopy both finds and removes a polyp in one sitting, which is why it occupies a special place. Risk rises with age, a family history, long-standing inflammatory bowel disease, and inherited conditions such as Lynch syndrome and familial adenomatous polyposis; smoking, heavy alcohol use, obesity and diets heavy in processed meat are also associated. When a cancer is found, how far it has grown through the bowel wall and whether it has reached lymph nodes define its stage, as in stage I colorectal cancer.
Also known as
Used in a sentence
A colonoscopy performed for screening identified a mass later confirmed to be colorectal cancer.
Good to know
Removing a polyp before it becomes malignant is the reason colorectal screening can prevent cancer rather than only detect it once it has developed.
Word origin
Where “colorectal cancer” comes from
Formed from colo-, from Greek kolon, meaning colon, and rectal, from Latin rectum, meaning straight, describing the final segment of the large intestine.