Screening starts at 45, and the point is removing polyps

Colorectal cancer develops in the tissues of the colon or rectum. The colon
is the first and longest part of the large intestine, absorbing water and some
nutrients and turning waste into stool; the rectum is the lower part, where
stool is stored. Cancer beginning in either may be called colorectal cancer.

Why screening is different here

Most cancer screening finds cancer earlier. Colorectal screening does that
and something better: it finds adenomas — colorectal polyps that look
abnormal under a microscope or are 1 cm or larger. **Adenomas are not cancer,
but they can turn into cancer over time**, and they can be **removed before
they do**.

That is why "having polyps removed before they can become cancerous" appears
on the prevention list rather than the treatment list.

Most experts recommend starting at 45 and continuing until at least 75.
Over 75, and for anyone at high risk, how often and which test is a
conversation with a provider. The tests are various stool tests, and
procedures — colonoscopy and flexible sigmoidoscopy.

What raises the risk

• Age — risk rises as you get older
• A personal or family history of colorectal cancer
• A history of adenomas
• A genetic syndrome — familial adenomatous polyposis (FAP) or **Lynch
  syndrome**
• Chronic ulcerative colitis or Crohn disease for 8 years or more
• Three or more alcoholic drinks a day
• Smoking
• Being Black — Black people have an increased risk of colorectal cancer,
  and of death from it, compared with other races
• Obesity

Colorectal cancer happens when DNA changes. Often those changes happen during
life and the exact cause is unknown; some are inherited.

Symptoms

It may not cause symptoms, especially at first — which is the argument for
screening on a schedule rather than on a feeling. Where there are symptoms:

• A change in bowel habits lasting more than a few days: diarrhoea,
  constipation, a feeling that the bowel does not empty completely, or stool
  that is narrower or a different shape than usual
• Blood in the stool — bright red or very dark
• Frequent gas pains, bloating, fullness or cramps
• Weight loss for no known reason
• Fatigue

Treatment

Surgery, radiation and chemotherapy, plus targeted therapy, which
mainly attacks specific cancer cells and spares normal ones, and
immunotherapy. For rectal cancer there is also active surveillance —
regular tests, with treatment aimed at cure if the cancer starts to grow.

Prevention

Avoiding the risk factors you control helps: not smoking, **limiting
alcohol to under three drinks a day**, managing your weight. Beyond that:
regular screening, **having polyps removed before they can become
cancerous**, and regular exercise.

Source: MedlinePlus, U.S. National Library of Medicine.