How Lifestyle and Screening Shape Colorectal Cancer Risks Across Generations

A RAND Corporation study analyzed colorectal cancer trends in the U.S. from 1978 to 2017, revealing declining rates in older adults due to widespread screening but rising early-onset cases linked to lifestyle changes in younger cohorts. The findings emphasize the need for expanded preventive measures and tailored screening strategies to address these diverging trends​

A study led by researchers at the RAND Corporation and published in the American Journal of Epidemiology delved into colorectal cancer (CRC) incidence trends in the United States using SEER data from 1978 to 2017. The researchers aimed to unravel how age, diagnosis periods, and birth cohorts impact CRC risks, employing a two-stage modeling approach. This analysis revealed contrasting trends: while CRC rates have steadily declined among adults aged 50 years and older, largely due to widespread screening programs, a troubling rise in CRC cases among those under 50 highlights an emerging public health concern. Early-onset CRC now demands attention as a critical area for both research and intervention.

Rising Risks for Younger Generations

The study found that individuals born in later cohorts face significantly heightened CRC risks. For instance, those born between 1983 and 1992 had over double the risk of rectal cancer and nearly twice the risk of distal colon cancer compared to individuals born between 1943 and 1952. Even proximal colon cancer, historically less affected by environmental factors, showed a 30% increase in risk for the younger cohorts. Unlike older adults, who have benefited from robust screening programs, the rise in CRC among younger individuals is primarily attributed to birth cohort effects. Changes in diet, physical activity, and broader lifestyle factors, such as increased consumption of processed foods and sedentary habits, may be fueling this trend, though definitive causes remain unclear.

Screening's Role in Driving Down CRC Rates for Older Adults

For individuals aged 45 years and older, the study underscored the transformative impact of screening, particularly colonoscopy, in reducing CRC rates. Screening uptake surged following Medicare’s decision in 2001 to cover colonoscopy for all beneficiaries, leading to a marked decline in CRC incidence. By 2015, screening rates had climbed to 61.3%, reflecting successful public health campaigns. Screening has proven particularly effective in reducing risks for rectal and distal colon cancers by identifying and removing precancerous lesions. However, the research highlighted a concerning limitation: screening appears to be less effective for proximal colon cancer, which showed a more modest decline in incidence compared to other CRC subtypes. This finding points to the need for enhanced detection methods tailored to proximal cancer.

Diverging Trends Between Younger and Older Adults

The study revealed stark contrasts between younger and older age groups in CRC trends. Period effects, driven largely by advances in screening, played a significant role in reducing risks for older adults but had no detectable impact on individuals under 45 years, where screening is rare. Younger cohorts experienced a steady increase in CRC risks, driven by birth cohort effects rather than immediate environmental or healthcare-related changes. The data suggest that societal shifts, such as rising obesity rates and dietary changes, may disproportionately impact younger generations, underscoring the need for targeted prevention strategies.

A Path Forward: Balancing Screening and Prevention

The researchers emphasized that addressing CRC's dual trends requires a multifaceted approach. Lowering the recommended age for CRC screening to 45, as recently endorsed by the U.S. Preventive Services Task Force, represents a pivotal step toward earlier detection. However, the study also calls for broader preventive measures aimed at mitigating lifestyle and environmental risk factors, particularly for younger populations. Beyond lifestyle changes, advancing technology to improve the effectiveness of screening for proximal colon cancer is critical. The findings underscore the importance of continuing research into CRC etiology and developing strategies that address the evolving burden of the disease across all age groups.

This comprehensive study employed a two-stage modeling approach to address the challenges of analyzing age, period, and cohort effects, which are closely interrelated. The first stage focused on birth cohort effects among individuals under 45 years, while the second stage used a Bayesian model to estimate period effects for those aged 45 and older. The researchers acknowledged the inherent complexities of disentangling these effects, emphasizing the importance of cautious interpretation. Their findings provide a nuanced understanding of CRC trends and offer actionable insights for public health policy, particularly in adapting screening and prevention efforts to meet the needs of different age groups and birth cohorts.

With CRC increasingly affecting younger populations, these findings highlight the urgency of a comprehensive approach that integrates early detection, innovative technologies, and lifestyle interventions. The study serves as a crucial roadmap for optimizing prevention strategies and ensuring that efforts to combat CRC are inclusive and forward-looking.