Causes

Doctors aren't certain what causes most colon cancers.

In general, colon cancer begins when healthy cells in the colon develop changes (mutations) in their DNA. A cell's DNA contains a set of instructions that tell a cell what to do.

Healthy cells grow and divide in an orderly way to keep your body functioning normally. But when a cell's DNA is damaged and becomes cancerous, cells continue to divide — even when new cells aren't needed. As the cells accumulate, they form a tumor.

With time, the cancer cells can grow to invade and destroy normal tissue nearby. And cancerous cells can travel to other parts of the body to form deposits there (metastasis).