colon cancer
Meaning of colon cancer: Few cancers offer such a long warning: the polyp stage lasts years, and removing one prevents the cancer that would have followed.
Definition of colon cancer
Colon cancer is a malignant growth arising in the lining of the colon, the long main section of the large intestine. Most begin as a polyp, a small benign growth on the inner surface, which accumulates genetic changes over years until some of its cells turn cancerous. The great majority are adenocarcinomas, arising from the mucus-producing glandular cells of that lining.
How does a polyp turn into cancer?
Not every polyp is on that road. Small hyperplastic polyps rarely progress at all, while adenomas and sessile serrated lesions are the types that can, and the risk rises with their size and number. The change is stepwise: a cell in the lining acquires a fault in a growth-control gene, its descendants outgrow their neighbors, further faults accumulate in the enlarging clump, and eventually one cell line breaks through the thin layer beneath the surface. That sequence typically unfolds over years, which is the window that makes removing polyps worthwhile. Because the colon and the rectum behave similarly, the two are often grouped together as colorectal cancer, though tumors low in the rectum are managed differently.
How does it spread?
| Stage of spread | Where the tumor has reached |
|---|---|
| Confined | The lining and the layer immediately beneath it |
| Through the wall | Into or beyond the muscle coat of the bowel |
| Regional | Lymph nodes alongside the supplying blood vessels |
| Distant | Most often the liver, then the lungs |
The liver comes first because blood leaving the bowel travels there directly through the portal vein before rejoining the general circulation.
What raises the risk, and how does it show?
Age is the largest factor. A close relative with the disease raises it, and a small share of cases come from inherited conditions such as Lynch syndrome or familial adenomatous polyposis, in which polyps form in great numbers from a young age. Long- standing inflammatory bowel disease affecting the large intestine raises it too, as do smoking, heavy alcohol use and obesity. Symptoms depend on position: a tumor on the left side narrows a tube already carrying formed stool, so it changes bowel habit or causes visible bleeding, while one on the right side sits where the contents are still liquid and may announce itself only through iron deficiency anemia from slow, unseen blood loss.
Also known as
Used in a sentence
A colonoscopy identified a mass later confirmed as colon cancer on biopsy.
Good to know
Most colon cancers develop gradually from a precancerous polyp rather than appearing abruptly, which is why detecting and removing polyps is directed at that specific stage of development.
Word origin
Where “colon cancer” comes from
Formed from colon, from Greek kolon, meaning the large intestine, and cancer, from Latin cancer, meaning crab, a name long applied to malignant tumors.