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Understanding Racial Disparities in Colon Cancer May Lead to More Targeted Prevention and Treatment

At a Glance

  • UVA researchers are leading research examining epigenetic aging of the left and right colon.
  • The study has provided insight into why African Americans are more frequently diagnosed with the more aggressive right-sided colon cancer.
  • Research showed that the right side of the colon ages faster in African Americans, while the left side ages faster in European Americans.
  • A new, larger study will take this a step further, looking at the lifestyle and environmental factors that may contribute to the increase in colon cancer diagnoses among young African Americans.

Although the overall incidence rate of colorectal cancer is falling in the U.S., it is increasing in young adults, particularly young African Americans. The American Cancer Society reports that African Americans are 20% more likely to develop colorectal cancer and 40% more likely to die from it. A team of scientists at UVA Cancer Center, led by cancer researcher and family physician Li Li, MD, PhD, has initiated research analyzing epigenetic aging of the left and right colon that has provided insight into this racial disparity and may lead to a more targeted approach to prevention and treatment.

Left- vs. Right-Sided Colon Cancer

Advanced age is a risk factor for many diseases, including colorectal cancer, Li reminds. Yet we now know a patient’s birth age is only part of the equation. Early research has shown that we also have to consider biological age of tissues to determine the health of an organ. This background discovery drove Li’s efforts to pinpoint how the colon ages — more specifically, how each side of the colon ages in European Americans and African Americans. That distinction was key to a critical discovery.

“We’ve come to realize that left- and right-sided colorectal cancers are two distinctly different diseases even though they are both colon cancers. Right-sided colon cancer is more aggressive and has worse outcomes,” says Li, leader of the Cancer Control and Population Health program at UVA Cancer Center. “African Americans tend to have more right-sided cancers compared to European Americans, who more often develop the disease on the left side.”

Discovering the Epigenetic Changes Impacting Colon Aging

With support from a National Cancer Institute Cancer Disparities SPORE P20 Planning Grant for research, Li and his team launched a study to find out why African Americans are at increased risk for this more deadly right-side colon cancer. 

The researchers collected tissue samples from the normal, right- and left-side colons of 128 patients — 88 Black and 40 European Americans. They then performed epigenome DNA methylation analysis of the tissue, looking at the epigenetic changes that come with age. What they found was that the right side of the colon in most African Americans had a unique pattern of hypermethylation, affecting gene expression. It was, in essence, like the right side of the colon was old beyond its years. 

“For African Americans in the study, the right side of the colon aged much faster than the left in the same person,” says Li. “The right-side colon was about 1.5 years older than the left.”

This, the researchers believe, could contribute to the increased cancer risk for African Americans and explain why they are more likely to develop cancerous lesions on the right side.

The research could also explain why younger people of European descent are more likely to develop lesions on the left side — the side that tends to age faster in that group. “For European American patients, our analysis showed it was the left side of the colon that aged faster; it was about 1.9 years older than the right,” says Li.

“This discovery provides novel insight of the mechanistic underpinning for the observed racial disparities in age-of-onset and anatomical distribution of colon neoplasia. Side-specific biological aging of the colon might emerge as a novel biomarker to guide the development of personalized prevention and intervention strategies,” he adds.

A New Study: Environmental & Lifestyle Factors Driving Racial Disparities in Colon Cancer

The challenge, of course, is understanding why these differences exist. “What drives this distinction across the two races? That’s where we are now,” says Li. “We need to understand why this happens; what is the underlying driver for the racial disparity?”

To address these outstanding questions, Li and his team are in the process of launching a new, larger study he hopes will provide insight into how environment and lifestyle play a role in colon cancer rates. 

A Reminder: Updated Screening Guidelines

The U.S. Preventive Service Task Force (USPSTF) now recommends that screening for colorectal cancer in average-risk adults begin at age 45 rather than 50. The revised guidelines were published in the Journal of the American Medical Association (JAMA) in May 2021.

“We aim to begin recruiting another cohort of patients for this study soon,” he says. “We will prioritize the inclusion of patients who come from rural areas and who identify as African American or minority so that we reach that data set. This way we can validate the findings we already have, but also start to acquire more omics-based data.”

The study will evaluate a patient’s upper stream social environment, stress and individual lifestyle factors such as diet and exercise, but will also drill down into other mechanisms that may be involved in the aging process, such as metabolism and the makeup of the microbiome. “This research focuses on the intersection of biology and environmental factors in the population,” says Li. 

“In addition to asking patients about their diet, physical activity, sleep habits, stress and living environment, we also hope to take biosamples — hair, fingernails, saliva — that will allow us to look for biological biomarkers and trace elements from the environment. We believe the outcome will have a lot of implications for prevention.”

Li and his team published their findings on the aging colon in the Journal of the National Cancer Institute

Originally published June 20, 2021. Updated Nov. 29, 2021.

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