Published early online in the ACS' CA: A Cancer Journal for Clinicians, the organization said this change from its previous recommendation that screening start at age 50 was partially based on data showing that CRC rates have increased in young and middle-age populations.
Specifically, the ACS said in a press release that its recommended starting age of 45 was based on "CRC incidence rates, results from microsimulation modeling that demonstrated a favorable benefit-to-burden balance of screening beginning at age 45, and the expectation that screening will perform similarly in adults ages 45-49 as it does in adults for whom screening is currently recommended (ages 50 and older)."
The new guideline differs from the latest recommendation by the U.S. Preventive Services Task Force (USPSTF) -- released in June 2016 -- which recommends that screening for CRC begin at age 50 and continue through age 75 -- an "A" recommendation.
The AAFP's own CRC screening recommendation agreed with that of the task force in recommending that patients ages 50-75 be screened. But the Academy graded its recommendation a "B" and differed from the task force by offering a preferential recommendation for specific screening tests.
The ACS guideline recommends that adults 45 and older who have an average risk for CRC undergo regular screening with either a high-sensitivity stool-based test or a structural (visual) exam, depending on patient preference and test availability.
The ACS acknowledged that the recommendation to screen those ages 45-49 is graded as a "qualified recommendation," reflecting the fact that the conclusion relies on the use of modeling without evidence from clinical trials. Most published clinical studies of colorectal cancer screening investigate screening only in those 50 and older. The recommendation for regular screening in adults ages 50 and older, on the other hand, is designated as a "strong recommendation" based on the quality of the evidence supporting it.
Jennifer Frost, M.D., medical director for the AAFP's Health of the Public and Science Division, told AAFP News: "Qualified recommendations indicate less certainty about the balance of benefits and harms of screening. There is clear benefit for older adults, but the data is lacking for younger adults."
It's also worth noting that although the ACS' new guideline doesn't prioritize different CRC screening tests, the AAFP did prioritize tests in its 2016 recommendation, saying the three tests supported by the best evidence regarding relative benefits and harms are fecal immunochemical tests, flexible sigmoidoscopy, and colonoscopy starting at age 50 and continuing until age 75.
Family physician Richard Wender, M.D., chief cancer control officer for the ACS and chair of the National Colorectal Cancer Roundtable, told AAFP News that CRC incidence has declined steadily during the past two decades in patients 55 and older because of screening that results in removal of polyps, as well as changes in exposure to risk factors. But there has been a 51 percent increase in CRC among those younger than 50 since 1994, and mortality rates among those younger than 55 group have also risen recently.
"This is deeply concerning," Wender said. "And part of the problem is they are not getting screened in their 40s."
Wender pointed to a recent analysis that found adults born around 1990 have twice the risk of colon cancer and four times the risk of rectal cancer compared with adults born around 1950, who have the lowest risk.
As for the modeling used to support the ACS' recommendation to lower the age to 45, Wender said the organization used the same models the USPSTF did for its final recommendation in 2016. Two of the microsimulation models used suggested that starting colonoscopy screening with an interval of 15 years at age 45 versus age 50 offered a slightly more favorable balance between the benefits and harms of screening.
Indeed, the USPSTF noted at the time it issued its recommendation statement that the Cancer Intervention and Surveillance Modeling Network (CISNET) CRC group models used estimated a modest increase in life years gained if screening were initiated at 45 instead of 50, Frost said.
"They pointed out, however, that this would also result in an increase of the lifetime number of colonoscopies, with associated potential harms," she added. "Because of this concern, and the lack of empirical evidence in younger populations, the USPSTF recommended starting screening at 50."
The ACS commissioned a new modeling study extending some of the CISNET-CRC group findings to incorporate data published since the USPSTF's 2016 recommendation. That study analyzed the rising incidence trends in younger adults and showed that multiple screening strategies beginning at age 45, including colonoscopy at the conventional 10-year interval, had a more favorable benefit-harm ratio with more life-years gained compared with starting screening at age 50.
"Lowering the starting age is expected to benefit not only the segments of the population who suffer disproportionately from CRC -- blacks, Alaska Natives and American Indians -- but also the white population considered to be at average risk," the guideline said. "Moreover, epidemiological trends in cohorts as young as those born in 1990 suggest that the higher risk of developing CRC will be a persistent concern for decades to come."
Interestingly, Wender said the risk for CRC seen today in those ages 45-49 is almost identical to that of those ages 50-54 when age 50 was first recommended as the age to begin CRC screening.
"That's why you have to constantly relook at these recommendations," he said. "(Dropping the screening age to begin at 45) adds zero to one colonoscopies in a lifetime. We are confident in the conclusion that starting screening earlier will prevent more colorectal cancer cases and deaths."
"I recommend at the very least that family physicians start colorectal cancer screening on time at age 50, as statistics show that currently isn't the case."
Wender also noted that until the USPSTF re-evaluates its recommendation age, patients ages 45-49 will likely not be covered by many insurers for CRC screening.
It's important to note that the ACS' recommendation to screen for CRC starting at age 45 is not based on clinical trials, said Frost.
"The ACS made this recommendation based on the increasing incidence of colon cancer in younger adults, with the assumption that screening would have similar benefits and harms in this age group as it does in older adults," she said. "They assumed that colon cancer in younger adults is similar to cancer that occurs in older adults, and that screening would have the same benefits and no additional harms."
The AAFP Commission on Health of the Public and Science's Subcommittee on Clinical Preventive Services will discuss the ACS guideline, but Frost said she didn't anticipate any change in the Academy's stance.
"Individual family physicians, in conversation with their patients, will decide whether earlier screening is appropriate. The AAFP will review empirical evidence once it is available.
"In the meantime, we will focus our efforts on increasing screening rates in individuals ages 50-75 and helping patients reduce their modifiable risks for colon cancer, which include tobacco and alcohol use, excess body weight and unhealthy dietary choices."