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Widespread adoption of an American Cancer Society (ACS) recommendation to initiate colorectal cancer screening at the age of 45 instead of 50 would save as many as 11,100 lives and cut the number of new cases of such cancers by more than 29,000 across the U.S. over 5 years, a modeling study indicated.

But it also suggested that greater benefit -- at a lower cost -- could be achieved by increasing the screening participation rates of older adults as well as persons at higher risk for colorectal cancer.

The study, led by , of Stanford University School of Medicine, was published .

Whereas incidence of colon and rectal cancer in older Americans has declined since the 1980s, a that individuals ages 40-49 have seen colon and rectal cancer incidence rates increase by 1.3% and 2.3%, respectively, over the last two decades. Such data prompted the last year that the age to start screening be dropped to 45. On the other hand, the as the general starting age for average-risk people (although an ).

Yet, the vast majority of colorectal cancers still occur in persons over the age of 50. And, at the same time, more than one-third of persons over the age of 50 don't participate in colorectal cancer screening in the U.S.

All this has raised the question: should physicians "focus on delivering [colorectal cancer] screening to 45-49 year-olds, concentrate on the large fraction of screen-eligible older people who are not currently being screened, or can they do both?" Ladabaum and colleagues wrote.

Their study used a validated Markov model to compare different screening and resource allocation strategies, and based their projections on screening participation rates and census data.

Over the next five years, they found, it would be possible to cut new cases and deaths substantially by starting screening at age 45 -- at the cost of conducting an additional 10.6 million colonoscopies and spending an extra $10.4 billion.

Increasing screening participation among 50- to 75-year-olds to 80%, meanwhile, would achieve nearly triple the benefit -- reducing the number of colorectal cancer cases by 77,500 and deaths by 31,800 -- with an added cost of just $3.4 billion.

As to the cost-effectiveness of initiating screening at the age of 45, Ladabaum and his colleagues compared its potential costs and benefits by modeling different screening strategies, such as administering colonoscopy every 10 years, annual fecal immunochemical testing, and sigmoidoscopy at age 45, followed by other tests in subsequent years.

In these analysis, the researchers found costs of $2,500 to $55,900 to gain one quality-adjusted life-year, making it clearly cost-effective to set the age to start screening at 45.

However, "the broader societal perspective is arguably more important than the narrower cost-effectiveness question," Ladabaum and colleagues wrote. "Our analyses demonstrate that given the choice over how to deploy a fixed number of colonoscopies, the clinical benefits would be far greater if screening were performed among the 44% of 55 year-olds and 37% of 65-year-olds who remain unscreened, or if colonoscopies were allocated to improve colonoscopy completion after abnormal FIT, than if average-risk screening were initiated at age 45."

the ACS's vice president for cancer screening, told 番茄社区app that when the group updated its guidelines "it subjected them to very rigorous modeling, which showed that strategies beginning at age 45 were significantly more efficient in benefits and outcomes than strategies beginning at the age of 50."

He added that one commonly overlooked factor is that of a "birth cohort effect" in which younger adults not only are experiencing a steeper increase in colorectal cancer than older persons, but that the incidence of colorectal cancer is increasing at a steeper rate for every birth cohort under the age of 55.

"That means that the higher incidence we are seeing in the 45 to 49 age group is an increase in incidence that will steadily get worse as time goes by," he said. "And we're already at the point that the incidence rate at age 45 today is just about where it was at age 50, 20 years ago."

He also pointed out that while Ladabaum and co-authors argued that focusing more on unscreened adults over the age of 50 might be a better a better use of resources, they also acknowledged that initiating screening at age 45 is cost-effective.

"Our argument is that colorectal cancer is the second leading cause of death among men and women when you look at the rates combined," Smith said. "So, this is not an issue of carving the pie into different sized slices, it's a challenge of getting a bigger pie."

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