What Is Colorectal Cancer?

Colorectal cancer is a cancer that starts in the colon or the rectum. These cancers can also be named colon cancer or rectal cancer, depending on where they start. Colon cancer and rectal cancer are often grouped together because they have many features in common.

Cancer starts when cells in the body start to grow out of control. Cells in nearly any part of the body can become cancer, and can spread to other areas of the body.

Causes

In most cases, it's not clear what causes colon cancer. Doctors know that colon cancer occurs when healthy cells in the colon develop errors in their genetic blueprint, the DNA.

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).

Symptoms

Symptoms of colorectal cancer include:

• changes in bowel habits
• diarrhea or constipation
• a feeling that the bowel does not empty properly after a bowel movement
• blood in feces that makes stools look black
• bright red blood coming from the rectum
• pain and bloating in the abdomen
• a feeling of fullness in the abdomen, even after not eating for a while.
• fatigue or tiredness
• unexplained weight loss
• a lump in the abdomen or the back passage felt by your doctor
• unexplained iron deficiency in men, or in women after menopause

Most of these symptoms may also indicate other possible conditions. It is important to see a doctor if symptoms persist for 4 weeks or more.