Frontline Cancer: Doctors debate best age to screen for colon cancer

FRONTLINE CANCER:

For some years, the rate of new colorectal cancer (CRC) cases in the United States has been dropping, thanks to increased screening. Men and women were advised to start getting colonoscopies at age 50, with follow-up frequency dependent on findings.

Then last year, a study led by American Cancer Society (ACS) researchers reported that new CRC cases were increasing among young and middle-aged adults. Indeed, once age was taken into account, those born in 1990 had double the risk of colon cancer and quadruple the risk of rectal cancer compared to people born around 1950, when risk was lowest.

That prompted the ACS to update its CRC screening guidelines, lowering the recommended age to begin screening from 50 to 45 years for people at average risk. (Persons at higher risk, such as those with a family history of CRC, should begin screening sooner, at 40 or even earlier.) But two other organizations that issue similar guidelines — the U.S. Preventive Services Task Force and the U.S. Multi-Society Task Force — have not changed their recommendation to start screening at age 50.

These public guidelines are important. They often become early, fundamental drivers to change and improved public health. The steady decline in CRC cases over the last decade is attributed, in large part, to people getting screened. But there remains debate and unanswered questions about what the 2017 ACS study about rising rates among younger people really says — and more importantly, what the change in ACS guidelines might portend.

In a recent paper, published in the journal Gastroenterology, a team of national experts, led by corresponding author Samir Gupta, M.D., an associate professor of medicine and gastroenterologist at Moores Cancer Center at UC San Diego Health, explored potential consequences of recommending persons be screened for colorectal cancer first at age 45.

Not surprisingly, for a subject as complicated as this, their assessment was mixed.

On the positive side, they speculated early initiation of screening might result in more CRC cases detected and more CRC deaths prevented in younger persons. They noted this might be especially important for some racial and ethnic groups, such as blacks and Alaska Natives, who have a higher risk for young onset cancer. They also suggested that earlier screening might lead to more consistent, repeat screenings later in life.

But they raised concerns about potential unfavorable or unintended consequences in recommending screening at age 45 instead of 50 as public health policy.

For one thing, it might mean limited resources would be diverted to lower-risk, younger populations and away from higher-risk, older populations. For example, the incidence rate among 45- to 49-year-olds, even with the recent increase in CRC rates, is 34 per 100,000 persons. But for people aged 50 to 54, the incidence rate is almost double: 60.2 per 100,000; and quadruples by age 70 to 74: 143.5 per 100,000. Marshaling the majority of effort for those at highest risk arguably produces the maximum benefit.

Also lowering the age recommendation might exacerbate existing CRC disparities because younger adults who act on the new screening recommendation might be less likely to belong to the racial/ethnic, socioeconomic or geographic groups at greater risk of CRC.

There's a broader financial implication too. Lowering the age recommendation would increase the screening pool by 22 percent, adding 21 million 45- to 49-year-olds to the 94 million 50- to 75-year-olds currently eligible for CRC screening. That means a lot more colonoscopies would need to be performed — not all necessarily covered by insurance.

Currently, it is unclear which of these possible outcomes will come to pass. Gupta and his colleagues call for caution in widespread implementation of recommendations for early screening for the entire population, and recommend that efforts to screen the highest risk populations, such as older individuals, those with a family history or those who are over age 50 who have never been screened intensify.

— Scott M. Lippman, M.D., is director of UC San Diego Moores Cancer Center. Reach him at mcc-dir-lippman@ucsd.edu

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