Colorectal Cancer Shifting Toward
Younger Adults

Pam Harrison

March 06, 2020

New statistics on colorectal cancer in the United States confirm previously reported trends showing the burden of disease is shifting toward younger adults.

The new data, published online March 5, come from latest edition of Colorectal Cancer Statistics from the American Cancer Society.

During the 2000s, the incidence of CRC has shown a rapid decline in individuals aged 65 and older, but has increased by 1% annually among those aged 50 to 64 years, and increased by 2% annually in those younger than 50 years, the report notes.

CRC death rates from 2008 through 2017 declined by 3% annually in individuals aged 65 years and older, and by 0.6% annually in individuals aged 50 to 64 years, but they have increased 1.3% annually in those aged younger than 50 years.

"As a result of declining [CRC] incidence in older age groups coinciding with increasing incidence in younger individuals, the CRC patient population as a whole is rapidly shifting younger," conclude the authors, led by Rebecca Siegel, MPH, scientific director, Surveillance Research, American Cancer Society, Atlanta, Georgia. 

Commenting on the new figures, Kimmie Ng, MD, MPH, Dana-Farber Cancer Institute, Boston, Massachusetts, who was not involved with the statistical report, said, "The new American Cancer Society statistics reinforce previous trends that demonstrate a very concerning, steady rise in the incidence of young-onset colorectal cancer."

This rising burden on people younger than 50 years old is what keeps me up at night. Dr Kimmie Ng

"This rising burden on people younger than 50 years old is what keeps me up at night, and which is why we have redoubled our efforts to tackle the problem," Ng told Medscape Medical News.

This effort includes the opening of the Young-Onset Colorectal Cancer Center at her institution a year ago, where Ng serves as the director. 

At the center, providers are partnering with patients to address their unique needs and to carry out focused research aimed at identifying those at the highest risk for CRC as well as novel treatment strategies. 

"Up until this point, there has been very limited scientific data available on CRC specifically in people younger than 50," Ng noted.

"And we are working every day to make inroads in decreasing CRC incidence and mortality by raising awareness of what is a potentially preventable cancer, and underscoring the importance of screening tests," she added.

The increase in CRC incidence among adults younger than 50 has also been seen in other countries, including Australia, New Zealand, Canada, and many across Europe, as reported by Medscape Medical News.   

CRC Statistics Reveal a Shift

In terms of overall numbers, the majority of cases are still occurring in older individuals.

The report estimates that the overall number of newly diagnosed CRC patients in 2020 in the US is expected to reach 147,950. Of these, 12% are expected to occur in patients younger than 50. Additionally, the authors estimate there will 53,200 deaths from CRC in 2020; about 7% are expected to occur in patients younger than 50.

Important to note, the authors say, is that there has been a shift toward CRC incidence in younger adults.

This is reflected by the median age at the time of diagnosis, which has dropped from age 72 years in the period 2001-2002 to age 66 years in the period 2015-2016, they add.

The decline in CRC incidence in older adults is explained by the authors as a result of increased screening.

They note that rapid declines seen in the 2000s in the incidence of CRC in people age 50 and older reflect a surge in screening colonoscopy, which tripled from 20% in 2000 to 61% in 2018 in this age group.

More recently, however, the decline in CRC incidence was confined to those aged 65 years and older, among whom CRC incidence rates dropped by 3.3% a year between 2011 and 2016.

This has not held true for patients between the ages of 50 and 64 years. In this age range, the declines in the incidence of CRC of between 2% to 3% a year during the 2000s have now reversed, and increased by 1% a year in the period 2011 through 2016, the researchers note.

"The uptick is similar to the trend in individuals aged younger than 50 years and likely reflects elevated disease risk in generations born since 1950 being carried forward by aging birth cohorts, a phenomenon referred to as a birth cohort effect," the authors write.

Asked to elaborate on this so-called "birth cohort effect," Siegel explained that the underlying risk of being diagnosed with CRC exclusive of the impact of screening had been declining for a long time because of changing patterns in risk factors such as a drop in smoking rates and increases in the use of anti-inflammatory drugs.

"However, this changed with people born after the 1950s; their risk of disease is higher and has increased with each subsequent generation," Siegel told Medscape Medical News in an email.

"People don't just have a higher risk when they're young and leave it behind as they age…they carry the elevated risk with them, which is why you see an uptick in CRC incidence over time in increasing age groups," she explained.

"Since 1950, risk has been increasing for every subsequent generation," Siegel emphasized.

Indeed, the report shows that CRC incidence rates in patients younger than age 50 have actually been increasing since the mid-1990s, largely driven by rectal tumors.

However, between 2012 and 2016, incidence rates for patients younger than 50 rose by 1.8% a year for tumors in the proximal and distal colon as well as in the rectum, and by 2.2% annually for total colorectum (excluding the appendix).

Alarmingly, "the increased incidence in those aged younger than 50 years is confined to advanced-stage diagnoses and is steepest among non-Hispanic Whites (NHW) [at] 2% per year and American Indian/Alaska Natives (AI/ANs) [at] 2.2% per year," the researchers note.

As a result of these trends, "CRC incidence rates in NHWs aged 20 to 49 years are now equivalent to those in blacks...despite being 40% higher in blacks during 1995-1996," they add.

Slightly more than 20% of patients between 45 and 49 years of age availed themselves of screening colonoscopy in 2018, as is now recommended by the American Cancer Society (many other medical associations, however, continue to recommend starting colonoscopy at age 50). There is an ongoing debate about whether the age to start screening for CRC should be lowered in the US. In other countries (eg, the United Kingdom), screening for CRC starts at 60 (using stool tests). 

However, the authors also note that "patterns of CRC test use do not appear to explain the rise in early-onset CRC, particularly in light of the preponderance of advanced-stage disease diagnoses."

Asked what she thinks is driving the shift of CRC incidence in younger patients, Siegel admitted that reasons for the rise are still unknown.

"The obesity epidemic is probably contributing to it but it doesn't seem to be the sole cause," she said.

However, diet has a large influence on CRC risk as well; there is considerable interest now in looking at how things like antibiotics influence gut health — specifically their role in determining the microorganisms that make up the microbiome, which could influence CRC risk, Siegel suggested.

Siegel and five other authors of the report are employed by the American Cancer Society, which receives grants from private and corporate foundations, including foundations associated with companies in the health sector for research outside of the submitted work. Author Andrea Cercek serves on the advisory board for Bayer and Array Biopharma and receives research support from Tesaro, RGenix, and Seattle Genetics, all outside the submitted work.

CA Cancer J Clin. Published online March 5, 2020. Full text

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