Increase in CRC in Young Adults in Many High-Income Countries

The dramatic increase in colorectal cancer (CRC) in younger adults that was reported in the United States is also seen in many other high-income countries, according to a new analysis that included data from 43 countries on six continents.

This study is the first high-quality, global analysis of trends in early onset CRC, according to the authors. It was published online on September 5 in Gut.

The findings are in sharp contrast to the trend among older adults, where CRC rates are declining or stabilizing, most likely in response to preventive screening programs.

"These patterns potentially signal changes in early-age exposures conducive to large bowel carcinogenesis and highlight an urgent need for research to explore the potentially unique etiology of young-onset CRC," author Rebecca Siegel, MPH, of the American Cancer Society in Atlanta, Georgia, said in a press release.

Disease trends in young age groups are a key indicator of recent changes in risk factor exposures. Rebecca Siegel, MPH

"Although the absolute risk of CRC in adults younger than 50 years is low relative to older adults, disease trends in young age groups are a key indicator of recent changes in risk factor exposures and often foreshadow the future cancer burden," she continued.

CRC represents the third most common cancer worldwide, with about 1.8 million new cases in 2018, according to background information in the article.

Rates of CRC have been increasing in low- and middle-income countries, most likely related to adoption of western lifestyles.

In contrast, CRC incidence has been stabilizing in higher income countries, especially in the countries that have CRC screening programs. However, the exception is the increase in CRC seen in younger age groups, for which the cause remains unknown.

Siegel and colleagues reported in 2017 on the dramatic increase in CRC among young adults in the United States.

At that time, Siegel told Medscape Medical News: "We think that the increase we're now seeing is likely related to the obesity epidemic."

But the picture is more complicated than that, because rates of CRC have increased in parallel with the obesity epidemic. If only obesity caused the trend, rates of CRC would be expected to increase 10 or 20 years after the obesity epidemic started, not at the same time. Most likely, other factors related to excess weight, such as a sedentary lifestyle and unhealthy diets, are independently affecting CRC, Siegel explained.

New Global Analysis

For the new study, Siegel and colleagues analyzed long-term data from high-quality, population-based cancer registries. The analysis compared CRC incidence among individuals aged 20 to 49 years and those aged 50 years and older. These individuals were diagnosed with CRC through 2012 and later for some of the countries with available data.

Over the past decade, the team found that CRC incidence among adults under age 50 increased in 19 countries of 36 countries that had enough CRC cases to be included in the analysis.

In nine of the countries that showed an increase in early onset CRC, the incidence of CRC among older individuals was either stable or decreased (Australia, Canada, Denmark, Germany, New Zealand, Slovenia, Sweden, United Kingdom, and United States).

South Korea had the fastest increase in the incidence of early onset CRC (average annual percent change [AAPC], 4.2; 95% confidence interval [CI], 3.4 - 5.0).

In most countries, the increase in early onset CRC began in the mid-1990s.

In Cyprus, Netherlands, and Norway, the rate of increase of early onset CRC was twice as fast as that seen in older individuals. For example, Norway had an AAPC of 1.9 (95% CI, 1.4 - 2.5) in the younger age group, compared with 0.5 (95% CI, 0.3 - 0.7) among those over age 50.

However, not all the countries included in the analysis showed this increase in early onset CRC. The incidence was stable in 14 countries, and it showed a decrease in three countries (Austria, Italy, and Lithuania).

The authors mention several potential limitations. The analysis lumped cancer of the appendix into CRC cases. Doing so may have affected the accuracy of results, because cancer of the appendix may have different characteristics than other types of CRC, they point out.

Also, the study did not have long-term data on CRC incidence for most countries, and it lacked high-quality data for many low- and middle-income countries.

Nevertheless, the authors conclude: "Improving awareness of the marked increases in young-onset CRC incidence could facilitate more diligent assessment of cancer family history by primary care clinicians, as well as follow-up of symptoms in young individuals, many of whom are diagnosed at a late stage."

Indeed, a recently reported survey of patients and survivors of young-onset CRC revealed that the disease is often initially misdiagnosed in these patients, which may explain why the disease is often advanced when it is eventually diagnosed.

The authors have disclosed no relevant financial relationships.

Gut. Published online September 5, 2019. Abstract

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