WASHINGTON (AP) — How old is too old for a colonoscopy? A surprising number of people older than 75 haven't ever been screened for colon cancer — and researchers reported Monday that it's not too late for them to get caught up.

Some may even consider screening into their 80s.

Colon cancer screening is powerful, credited not only with saving lives. The American Cancer Society recently calculated that over the last decade, new cases of colon cancer dropped significantly among middle-aged and older adults, thanks largely to increasing use of colonoscopies that allow removal of precancerous growths before tumors have time to form.

Some things to know about the latest research on colon cancer screening.

WHO SHOULD BE SCREENED?

National guidelines recommend regular checks starting at age 50 and going up to age 75. Nearly two-thirds have been appropriately screened for colon cancer, according to the latest government estimates.

WHAT ABOUT OLDER AMERICANS?

Those guidelines don't recommend routine screening after age 75. After all, a colonoscopy that delivers good news isn't supposed to be repeated for 10 years, because it takes so long for those precancerous polyps to become dangerous. Average life expectancy for an 80-year-old is eight to 10 years.

But the guidelines don't address the 23 percent of Americans over 75 who somehow missed out on screenings when they were a bit younger, before a colon check in your 50s and 60s had become the norm.


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Monday's study examines if it's worth starting screening so late, when most people already have at least a few other health problems, such as heart disease, that could affect whether detecting an early-stage colon cancer prolongs life.

THE FINDINGS

Researchers at Erasmus University in the Netherlands and New York's Memorial Sloan Kettering Cancer Center used computer modeling to compare the potential effects of different colon checks on 10 million previously unscreened people ages 76 to 90.

Someone who's very healthy should consider some form of screening up to age 86 — but even a person with severe health problems could benefit from a first-time check up to age 80, the team reported in Annals of Internal Medicine.

In the healthiest patients, a colonoscopy was the most effective choice up to age 83, while a stool test was the better choice for 85- and 86-year-olds, the researchers found.

The results are a bit surprising, said Dr. Richard C. Wender, the American Cancer Society's chief of cancer control.

"Our sense was, if we're going to screen beyond age 75, it should only be in very healthy people," said Wender, who wasn't part of the new study. "This model I think will help us give clearer advice to the public."

THE BIGGER MESSAGE

About 137,000 Americans will be diagnosed with colorectal cancer this year, the cancer society estimates. About 50,000 colon cancer patients will die.

Upper age limits aside, public health officials say not enough of the 50-and-older crowd get potentially life-saving checks. The cancer society's new campaign aims for a screening rate of 80 percent, up from two-thirds, by 2018.

"If you're polyp-free at 70, we have so dramatically reduced your likelihood of a death from colon cancer, you probably don't need to ever think about it again," Wender said.

THE CHOICES

With a colonoscopy, doctors use a long flexible tube to examine the colon and remove any polyps. While only needed once a decade, it can be uncomfortable and is the priciest option.

Studies show a home stool test done every year can be equally effective. (A third choice, sigmoidoscopy, uses a tube to examine the lower colon but isn't common in the U.S.)

In the new study, stool testing was a better value for the oldest patients because it targets larger polyps "that have a shorter period of time before they become a real threat," Wender explained.

But individual choice matters: "There's a test out there for everybody," he said.