Colon Cancer on the Rise in Young Adults: A Growing Concern

Colorectal cancer (colon or rectal cancer), traditionally viewed as a disease of older populations, has been showing a disturbing increase in incidence among young people (Figure 1). This trend, evident in recent decades, is prompting healthcare professionals and researchers to reevaluate risk factors and advocate for earlier and more vigilant screening measures.

Early-onset colorectal cancer (EOCRC) refers to colorectal cancer (CRC) diagnosed in individuals <50 years, and represents 10-12% of newly diagnosed CRC cases. The American Cancer Society has reported an alarming increase in EOCRC since the 1990s with the steepest rise seen in those aged 20-29. Research from the University of California San Francisco found that between 2004 and 2015, colon cancer incidence increased by 1-2% each year in adults aged 20-39. A 2022 study in the Journal of the National Cancer Institute found that adults born in 1990 have double the risk of colon cancer and quadruple the risk of rectal cancer (at a similar age) compared to those born around 1950. EOCRC is predicted to be the leading cause of cancer death in US individuals aged 20-49 by 2030.

Because it is unexpected, EOCRC is often diagnosed at an advanced stage with a predilection for left-side colon and rectum. Common symptoms include abdominal pain and rectal bleeding. The increase in EOCRC is in contrast to overall CRC incidence decreasing due to improved screening and prevention in older individuals.

Importantly, the trend is not limited to the United States. Similar increases in early-onset colon cancer have been reported in other high-income countries, suggesting that the factors contributing to this rise are likely widespread and not confined to a single region.

While the exact causes remain unclear, researchers are investigating potential factors such as changes in diet (increased processed foods, decreased fiber), sedentary lifestyles, obesity, environmental toxins, and changes in gut bacteria. These causes can be grouped into two general categories: environmental/lifestyle (i.e. all examples listed in previous sentence) and genetics.

Genetics can play a crucial role in the susceptibility of younger people to colon cancer. Those with a family history of the disease are at a higher risk, prompting experts to recommend earlier screening for these individuals. Recent advancements in genetic testing have made it easier to identify at-risk individuals, but there is still a considerable gap in public awareness and accessibility of such preventive measures. 

Possible genetic factors include higher prevalence of inherited cancer predispositions, especially Lynch syndrome which is caused by mutations in genes involved in DNA mismatch repair. As a result, cells in the afflicted subject have a higher mutation rate leading to more cancers. Up to 3-5% of all colorectal cancer is due to Lynch syndrome, and it is estimated that Lynch syndrome accounts for about 10-20% of early-onset CRC (EOCRC) cases. Depending on the mutation the lifetime risk of CRC can range from 10 to 60% in Lynch syndrome patients.

However, it is unlikely that the population genetics can change quickly enough to give rise to the rapid rise in EOCRC pointing the finger at environmental/lifestyle factors. Unlike older generations, many young adults today exhibit dietary habits that lean heavily towards processed foods and low in fiber, which are critical in maintaining a healthy digestive tract. Furthermore, increased sedentary behavior, higher rates of obesity, and excessive alcohol consumption are recognized as significant contributors to this trend. These lifestyle choices can lead to chronic inflammation in the colon, a known risk factor for the development of cancerous cells.

Environmental and lifestyle factors that may contribute to EOCRC include:

• Rising obesity rates and metabolic syndrome conditions linked to increased EOCRC risk
• Dietary habits that lean heavily towards processed foods and low in fiber, which are critical in maintaining a healthy digestive tract e.g. sugar-sweetened beverages, red and processed meat, Western-pattern diets
• Prolonged sedentary behavior and lack of exercise
• Excessive alcohol consumption
• Environmental toxins i.e. exposure to certain chemicals and pollutants

Finally there is the possibility of interactions between genetic and environmental factors that accelerate the carcinogenic process.

In terms of repercussions, the rise in EOCRC incidence has led medical experts and organizations to reconsider screening guidelines. For instance, the American Cancer Society updated its guidelines in 2018 to recommend that individuals at average risk of colon cancer begin regular screenings at age 45 instead of 50, a move intended to catch and prevent the disease in younger adults earlier.

Figure 1. Global incidence (across 204 countries) of early-onset colorectal cancer grouped by sociodemographic index (SDI, low to high) quintiles from 1990 to 2019. In total, there is roughly a doubling of incidence by the age-standardized measure which does not normalize for population growth (adapted from Fig. 5 of Pan et al. BMC Public Health, 2022).