Colorectal Cancer: Symptoms, Screening and Treatment

Colorectal cancer is cancer that starts in the colon (large intestine) or the rectum, the last few inches before the anus. People also call it colon cancer, rectal cancer or bowel cancer. Most cases begin as a small growth called a polyp that turns into cancer over about 10 years. Screening from age 45 can find and remove polyps before that happens, which makes this one of the most preventable cancers.

Key points

About 150,000 people in the US are diagnosed each year, and rates are rising in adults under 50.
Screening should start at 45 for most people, and earlier if you have a family history or other risk factors.
Colonoscopy, yearly stool tests and other options all work. Pick the one you are most likely to complete.
Warning signs include blood in the stool, a lasting change in bowel habits, belly pain, tiredness and weight loss.
When found early, about 9 in 10 people are alive 5 years later.

What causes colorectal cancer

Cells in the lining of the colon and rectum are replaced all the time. Over the years, gene changes can build up in some cells and make them grow into a polyp. A few polyps keep changing until they become cancer. The cancer can then grow through the bowel wall and spread to lymph nodes, the liver or the lungs.

Things that raise your risk:

Age 45 and older, though younger adults get it too
A parent, brother, sister or child with colorectal cancer or advanced polyps
Your own history of polyps or colorectal cancer
Ulcerative colitis or Crohn’s disease affecting the colon for many years
Inherited conditions such as Lynch syndrome or familial adenomatous polyposis (FAP)
Extra weight, little physical activity and type 2 diabetes
A diet high in red and processed meat and low in fiber
Smoking and heavy drinking

Black Americans have higher rates and are more likely to die of it, and people of Ashkenazi Jewish descent have a higher inherited risk.

Colorectal cancer symptoms

Early cancer often causes no symptoms, which is why screening matters. Signs to watch for:

Bright red blood on or in your stool, or stool that looks dark or black
Diarrhea, constipation or narrow stools that last more than a few weeks
Feeling that your bowel doesn’t empty all the way
Cramping, belly pain or bloating that doesn’t go away
Weakness and tiredness from low iron (anemia)
Losing weight without trying

Hemorrhoids, infections and irritable bowel syndrome cause many of these symptoms too. Don’t assume bleeding is from hemorrhoids, especially if you’re over 40 or it keeps happening. In women, anemia from slow bleeding is sometimes blamed on heavy periods, so ask about a bowel check if your iron is low.

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Screening for colorectal cancer

For people at average risk, screening runs from age 45 to 75. After 75, you and your doctor decide based on your health. Options include:

Colonoscopy every 10 years. A flexible camera checks the whole colon while you are sedated, and polyps are removed during the test.
Fecal immunochemical test (FIT) every year. You collect a small stool sample at home and mail it in.
Stool DNA test (such as Cologuard) every 1 to 3 years.
CT colonography (virtual colonoscopy) every 5 years.
Flexible sigmoidoscopy every 5 years, which checks only the lower colon.

A blood test for screening is also approved, but it finds fewer polyps than stool tests or colonoscopy. If any test other than colonoscopy is positive, you’ll need a colonoscopy to finish the check. People at higher risk usually start earlier and have colonoscopy more often.

How it’s diagnosed and staged

A colonoscopy finds the tumor and takes small samples (biopsies). Blood tests check for anemia and a tumor marker called CEA. A CT scan of the chest, belly and pelvis looks for spread. Rectal cancer also gets an MRI of the pelvis. The tumor is tested for gene changes, such as mismatch repair (MMR), KRAS and BRAF, which help choose treatment.

Stages run from 1, where cancer is only in the inner layers of the wall, to 4, where it has spread to distant organs such as the liver or lungs.

How colorectal cancer is treated

Colon cancer

Surgery removes the part of the colon with the cancer and nearby lymph nodes, often through small cuts. Very early cancers in a polyp can sometimes be removed during colonoscopy. Chemotherapy after surgery lowers the chance of the cancer coming back for stage 3 and some stage 2 cancers.

Rectal cancer

Many people get chemotherapy and radiation first, then surgery. If the tumor disappears completely, some can skip surgery and be watched closely instead. Tumors with MMR changes can respond very well to immunotherapy alone.

Advanced cancer

Chemotherapy, targeted drugs and immunotherapy can shrink the cancer and help people live longer. When spread is limited to a few spots in the liver or lungs, surgery or other local treatments can sometimes cure it.

Some people need an ostomy, an opening on the belly where stool leaves the body into a pouch. Many ostomies are temporary.

Lowering your risk

Get screened on time, and make sure family members know your history.
Stay active and keep a healthy weight.
Eat plenty of vegetables, fruit, beans and whole grains. Limit red and processed meat.
Don’t smoke, and limit alcohol.

When to see a doctor

Blood in your stool or black stools
A change in bowel habits lasting more than a few weeks
Belly pain, tiredness or weight loss without a clear cause
You are 45 or older and haven’t been screened

Get emergency care for heavy rectal bleeding, fainting, or belly swelling with vomiting and no stool or gas.

Common questions about colorectal cancer

Are all colon polyps precancerous?

No. Adenomatous polyps (adenomas) and sessile serrated polyps can turn into cancer, though most never do. Small hyperplastic polyps in the lower colon rarely do. Doctors can’t always tell by looking, so they remove polyps during colonoscopy and send them to a lab.

Are colon polyps common?

Yes. Doctors find at least one precancerous polyp in about a third of people over 50 who have a screening colonoscopy, and more in older adults. Having polyps removed lowers your cancer risk. Depending on their number and type, your next colonoscopy may be in 3 to 10 years.

Can thin stools and gas be a sign of colon cancer?

Usually not. Thin stools and gas most often come from constipation, diet changes or irritable bowel syndrome. Narrow stools that last for weeks, especially with bleeding, belly pain or weight loss, can be caused by a tumor in the lower colon or rectum and should be checked.

What is stage 4 colon cancer?

Stage 4 means the cancer has spread beyond the colon to distant organs, most often the liver, lungs or the lining of the belly. It is rarely curable, but treatment can control it, often for years. Some people with only a few spots in the liver or lungs are cured with surgery.