Genetics Could Explain Racial Disparity in Colon Cancer

African Americans half as likely as whites to have genetic marker linked to better colon cancer outcome

(RxWiki News) Colon cancer is one of the leading causes of cancer-related death in the United States and takes a significant toll on African Americans, who die from the condition more than any other racial group.

To better understand that disparity, researchers looked at risk factors for the disease, including a particular genetic marker.

That marker, according to the new study, appeared more often in Caucasians with colon cancer than in African Americans.

"Discuss colon cancer prevention and screening with a gastroenterologist."

John Carethers, MD, John G. Searle professor and chair of internal medicine at the University of Michigan Medical School in Ann Arbor, led this research.

Dr. Carethers and his research team set out to better understand why African Americans are more likely to die of colon cancer than Caucasians.

Colon cancer, which affects the body’s lower intestine, primarily begins in cells that make and release mucus. The National Cancer Institute estimated there are about 96,830 new cases diagnosed each year.

Symptoms of colon cancer include changes in bowel habits, rectal bleeding, dark stool, abdominal pain and unintended weight loss.

The researchers examined 503 patients who took part in the North Carolina Colon Cancer Study, which included rural and urban areas, and included people already diagnosed with the condition.

Of those 503 study participants, 45 percent were African Americans and 55 percent were Caucasian.

Further breaking down the groups, the researchers used tissue samples to identify a genetic marker called microsatellite instability (MSI), which is a predictor of cancer cells' resistance to certain chemotherapy treatments.

Despite that resistance, MSI colon cancer patients have better clinical outcomes than their counterparts who do receive chemotherapy.

MSI was present in 14 percent of Caucasians and 7 percent of African Americans, according to the study.

The researchers concluded that African Americans with colon cancer were half as likely to have MSI colon cancer, which is associated with better outcomes, than white colon cancer patients.

“We know that patients with MSI colon cancer do better without chemotherapy,” Dr. Carethers said in a prepared statement. “But these improved survival benefits are limited among African Americans with colon cancer.”

The researchers also found that African American colon cancer patients were more likely to have right-sided cancer than left-sided cancer.

Right-sided colon cancer, which refers to location in the organ, is harder to detect during screenings and is often more advanced when spotted.

Dr. Carethers called right-sided colon cancer the “black ice of the colon — unseen but potentially deadly.”

This study was published online June 23 in the peer-reviewed journal PLOS ONE.

Grant funding was provided by the National Institutes of Health and the National Cancer Institute’s Comprehensive Partnerships to Reduce Cancer Health Disparities.

The authors did not disclose any conflicts of interest.

Review Date: 
June 23, 2014