Colon and Rectal Cancer

What it is

Colorectal cancer starts in the colon or the rectum, the last part of the digestive system.

NCI describes how it usually begins: as a growth called a polyp on the inside wall. Most polyps never turn into anything. Some do, slowly, over years. And a polyp can be found and taken out during the same test that spots it.

That is why this cancer sits apart from the others on this list. Screening does not only find it earlier. Screening can stop it from happening.

What to watch for

NCI's list:

• Blood in the stool, either bright red or dark
• A change in bowel habits: diarrhea, constipation, stools narrower than usual, or a feeling that the bowel does not empty completely
• Belly discomfort: gas pains, bloating, fullness, cramps
• Losing weight without trying
• Feeling very tired
• Vomiting

NCI notes these can be caused by other conditions too, and most of the time they are. What matters is a change that lasts, especially bleeding.

What raises the risk

Things nobody can change: age. NCI says risk increases after 50. A first-degree relative with it, which roughly doubles risk. A personal history of colorectal cancer, of high-risk polyps, or of ovarian cancer. Inherited conditions such as familial adenomatous polyposis and Lynch syndrome. Long-standing inflammatory bowel disease, meaning ulcerative colitis or Crohn disease for eight years or more. Race, with Black Americans at higher risk.

Things that can change: heavy alcohol use, which NCI describes as three or more drinks a day. Smoking. Obesity.

NCI also lists protective factors, and puts it carefully: a lifestyle that includes regular physical activity is linked to a decreased risk. Daily aspirin for two years or more also shows a benefit, but one that emerges 10 to 20 years after starting, and aspirin carries its own risks. That is a decision for a clinician, not a page.

Is there a test before symptoms start?

Yes, and there is more than one, which is good news if the idea of a colonoscopy is what has been stopping you.

NCI lists the tests as fecal occult blood testing, DNA stool tests, sigmoidoscopy, colonoscopy, and virtual colonoscopy. NCI says some of these tests help find cancer at an early stage and may decrease deaths from the disease.

The US Preventive Services Task Force recommends screening for all adults aged 50 to 75, its strongest grade, an A. For adults 45 to 49 it gives a grade B, also a recommendation to screen. For adults 76 to 85 it gives a grade C, meaning the choice should take account of overall health, past screening, and what the person wants.

Which test, and how often, depends on the test chosen and on your own history. That part is worth asking about directly, because the least invasive option you will actually complete beats the best option you keep putting off.