Colorectal cancer (CRC) is one of the most common cancers worldwide and the second leading cause of cancer-related deaths, with more than 1.9 million new cases and approximately 904,000 deaths in 2022. While the incidence has stabilized or even declined among older adults over 50 years of age in many countries over the past decades thanks to screening and lifestyle changes, an opposite trend is evident among younger adults under 50 years of age.
The current study, published in The Lancet Oncology used high-quality population-based cancer registry data, and analyzes the incidence rates of colorectal cancer among younger adults (25-49 years) compared to older adults (50-74 years) in 50 countries and territories. The results show a significant increase in disease rates among young adults in 27 of the countries studied during the observation period up to 2017.
The largest increases in early-onset colorectal cancer were recorded in New Zealand (annual increase of 3.97%), Chile (3.96%), Puerto Rico (3.81%), and England (3.59%). Particularly noteworthy: In 14 countries the increase was limited exclusively to the younger age group, while the incidence among older people either remained stable or even declined.
The study also provides new insights into the geographical distribution of this phenomenon. While previous studies documented the increase primarily in Western industrialized countries, the current analysis shows that this trend is now also observed in countries in Latin America and the Caribbean (Argentina, Chile, Costa Rica, Ecuador, Martinique, and Puerto Rico), Asia (Israel, Japan, Thailand, and Turkey), and Eastern Europe (Belarus).
An interesting aspect of the study is the gender differences. In some countries, such as Chile, Puerto Rico, Argentina, Thailand, Sweden, Israel, and Croatia, the incidence increased faster among men than among women. In other countries, such as England, Norway, Australia, Turkey, Costa Rica, and Scotland, the increase was more pronounced among women.
The exact causes of the increase in early-onset colorectal cancer are not yet fully understood. Although genetic factors and family history play a more frequent role in younger patients, the majority of cases are sporadic. Studies point to several modifiable risk factors, including:
In fast-growing economies, rapid urbanization and the adoption of Western dietary habits may also contribute to the increase. For example, in South Korea, meat consumption increased 19-fold between 1961 and 2021, and in Japan, it increased seven-fold.
The increase in early-onset colorectal cancer also presents new implications for practice. Awareness of atypical presentations and younger patients is needed. Since most early-onset colorectal cancers are diagnosed symptomatically due to a lack of screening programs, increased awareness of suspicious symptoms in younger patients is crucial.
Rectal bleeding, abdominal pain, changes in bowel habits, and unexplained weight loss should also prompt further diagnostic investigations in younger adults. Increased awareness of risk factors and symptoms can help reduce delays in diagnosis.
Systematic family history assessment can also help identify high-risk patients. Studies suggest that up to 50% of early-onset colorectal cancers could be diagnosed earlier, and up to 16% could potentially be prevented, if colonoscopies were performed according to family history-based guidelines.
It may also be necessary to rethink screening recommendations in the long term. In the United States, the American Cancer Society lowered the recommended starting age for colorectal cancer screening from 50 to 45 years in 2018. In Australia, the starting age for the national colorectal cancer screening program was also lowered to 45 years, effective July 1, 2024. However, adapting screening recommendations to the changing epidemiology of colorectal cancer remains controversial, especially given limited resources.
In the long term, further research efforts are needed to better understand the causes of early-onset colorectal cancer and to develop preventive measures that are appropriate to local resources and cultural circumstances.