In the U.S. African-American men and women are diagnosed with and die from colorectal cancers at higher rates than men and women of any other racial or ethnic background. Now, a new study from the University of Michigan may provide insight into this disparity. African-Americans with colon cancer are half as likely as European-American patients to have a type of colon cancer that is linked to better outcomes and more likely to have right-sided cancers, researchers discovered.

Led by Dr. John M. Carethers, John G. Searle Professor and Chair of internal medicine at the University of Michigan Medical School, the team of researchers conducted a study involving 503 people with colon cancer. The researchers began by identifying patients using the North Carolina Colon Cancer Study, which collected data on patients throughout central and eastern regions of the state and so includes both rural and urban areas, creating an adequate representation of both African-Americans and rural residents. Among the overall group, 45 percent were black and 55 percent were white and all had suffered from colon cancer. For this important public health study, scientists had examined tissue samples taken during surgery and assessed them for various markers.

After analyzing the data from the North Carolina Colon Cancer Study, Carethers and his colleagues found that 14 percent of Caucasians and seven percent of African-Americans had a genetic marker known as microsatellite instability (MSI). "We know that patients with MSI colon cancer do better without chemotherapy. But these improved survival benefits are limited among African-Americans with colon cancer," said Carethers, explaining how MSI tumors are resistant to the chemotherapy drug 5FU, commonly used to treat colorectal cancers. These results, Carethers suggested, may help explain the overall disparity in cancer outcomes.

'Black Ice' of the Colon

Surprisingly, the researchers also found that African-Americans patients were more likely to have cancer develop on the right side of their colon. "Right-sided colon cancer may be the 'black ice' of the colon — unseen but potentially deadly," noted Carethers in a press release. Generally, right-sided colon cancer is easier to miss during screening and, when found, more likely to be more advanced than left-sided cancers. Armed with this knowledge about underlying genetics and right-sided development, scientists may be able to adjust their treatment practices and so correct any racial disparity in survival rates.

The American Cancer Society estimates there will be 96,830 new cases of colon cancer and 40,000 new cases of rectal cancer diagnosed in the U.S. during 2014. Because they have many features in common and may be treated in a similar fashion, colon and rectal cancers are generally lumped together as colorectal cancer. Overall, the lifetime risk of developing colorectal cancer is about one in 20 (five percent), with that risk being slightly lower among women than men. The wonderful news here is the death rate from colorectal cancer has been dropping for more than 20 years. Researchers believe this may be due to more people getting screened, which is recommended beginning age 50.

Source: Murali B, Yang B, Basa R, et al. Influence of Race on Microsatellite Instability and CD8+ T Cell Infiltration in Colon Cancer. PLOS One. 2014.