The Rising Incidence of Colorectal Cancer in Younger Adults

Blog post by Jasmin Skinner

Despite advances in screening, treatment, and associated improvement in survival rates, colorectal cancer (CRC) remains the third most common cancer diagnosis in both men and women in the United States. Currently, CRC is the second leading cause of cancer-related deaths, [1] and therefore understanding relevant risk factors is a vital public health concern.

While typically associated with older populations, in recent years, CRC has become more prevalent in the young. For example, the 2023-2025 Colorectal Cancer Report from the American Cancer Society reveals an increasing incidence in those aged 20-49 [1]. Perhaps surprisingly, in older populations the incidence of CRC is stagnant or declining, with the greatest decrease in CRC incidence observed in the oldest population group (65+). This is further supported by a 2022 study by Ahmed et al. demonstrating a seven-fold increase in incidence rates in young adults (under 40) over three decades, of which disproportionately affected female populations [2].

What further confounds this observed increase is that young people are also getting different kinds of colorectal cancers. Older generations typically develop right-sided tumors within the cecum, ascending, and proximal transverse colon, correlating with drops in estrogen associated with aging. In contrast, younger patients are more likely to develop it on their left side (descending and sigmoid) of their colon, as well as the rectum [3]. Of more concern, CRC diagnosis in younger individuals tends to occur at later stages of disease, often revealing a more aggressive form, and thus makes effective treatment more difficult. Regardless of cause, understanding the reasons behind this rise is crucial for developing targeted interventions and preventative measures to address this concerning trend. This article aims to consolidate current perspectives and evidence on the increasing prevalence of CRC in young populations. 

The most obvious reason for an increase in colorectal cancer in young people would be a decrease in screening age. While the average recommended age for CRC has dropped from 50 to 45 at the recommendation of the U.S. Preventive Services Task Force, this alone cannot contribute to the aforementioned cancer rate increases [4,5]. A 2023 publication from Kalyta et al. demonstrated that a decrease in CRC screening from age 50 to 40 or 45 had in fact resulted in a decreased incidence and risk of mortality from CRC, while also decreasing healthcare costs [6]. Advanced screening also usually only occurs for individuals who know they have a prior family history of colorectal cancer, however approximately 30% of all CRC cases have past family history of this disease, with only 5% having an identifiable heritable CRC syndrome [3]. The increase in CRC in young patients can therefore not be solely attributed to increased screening efforts.

The rise in colorectal cancer among young patients could be driven by changing nutrition and activity, as the largest declines in physical activity occur in adolescence, young adults, and those over 65 [7]. This has resulted in a global increase in the prevalence in digestive and metabolic issues, of which chronic intestinal inflammation and obesity have particular relevance to CRC.

Inflammatory bowel diseases (IBD), such as Crohn’s disease and ulcerative colitis, [1] cause chronic and prolonged inflammation and oxidative damage to the intestinal lining. Over time, the oxidative damage induced by reactive oxygen species could potentially alter the shape of a DNA strand and result in a cancerous mutation [8]. However, in a 2019 review of CRC in patients under 50, only 16% of the participants were identified as having a germ-line mutation, ultimately leading to more questions as to where the majority of these cases arise from. 

A common risk factor for other diseases and cancers, obesity, has also been demonstrated to be a notable risk factor for CRC. Increased adipocytes – fat cells – provide ample excess energy that cancerous cells could recruit for themselves [9]. According to the World Health Organization, adolescent obesity has risen from 8% in 1990 to around 20% in 2022, a more than two-fold increase [10].

Additionally, obesity often correlates with excess consumption of red and processed meats, which has been demonstrated to further elevate CRC risk by 20-30%. Studies have shown that high consumption of these foods can lead to the production of carcinogenic compounds in the gut [11]. Interestingly, the Heme protein, among other carcinogens, appears to be particularly aggravating to the intestinal tract, activating hyperproliferation in the colon epithelium and disbalancing beneficial and pathogenic bacteria [11].

All the previous risk factors cumulate to create the ideal conditions for an increasing incidence of CRC due to a shift in gut microbiota. The Heme protein has been demonstrated to be an important virulence factor for gut bacteria, as the inorganic iron from this protein acts as an essential growth factor for these bacteria [11]. Obesity has been demonstrated to decrease gut bacteria diversity, which has been demonstrated to increase the likelihood of intestinal cancers [12]. The solution to these changing gut diversities is actually rather simple, as increased consumption of fibrous foods has led to a decreased risk of CRC. A 2017 meta-analysis found that 90g/day of whole grains decreased CRC risk by 17% [13], likely from the antiproliferative and anti-inflammatory effects from butyrate produced from intestinal fiber fermentation [12]. While further preventative efforts are likely needed for individuals at high-risk for colorectal cancer, the essential immunosuppression provided by a diverse gut biota is becoming increasingly apparent.

The rising incidence of colorectal cancer (CRC) among younger populations, coupled with the aggressive nature of the disease in this age group, necessitates urgent action. Additional research is crucial to better understand the unique biological and environmental factors contributing to this trend. By identifying specific risk factors and developing targeted prevention strategies, we can improve early detection and treatment outcomes. Further lowering the recommended screening age for CRC and increasing awareness about the importance of early screening are essential steps in reducing the health burden of this disease on young individuals. Proactive measures for those at the highest risk, including lifestyle modifications and regular monitoring, will be vital in mitigating the impact of colorectal cancer for young patients.