Race may be a factor in colon cancer recurrence

Volume 5, Issue 1, 2016

Summary

Black people under 50 have more than double the risk of cancer recurrence compared with whites.

Photograph of Harry H. Yoon, M.D.

Harry H. Yoon, M.D.

The genetic makeup of colon cancer tumors and survival rates for patients with the disease differ by race, according to a study from researchers at the Mayo Clinic Cancer Center, published in the Journal of the National Cancer Institute in July 2015.

"These findings put the issue of race more prominently on the radar of investigators that cancer biology may contribute to race-based disparities," said the study's co-lead author, Harry H. Yoon, M.D., an oncologist with the Mayo Clinic Cancer Center. "While it is too early to change the way we treat these patients, our results indicate that future studies are needed to examine potential biological drivers of these differences more closely."

According to the American Cancer Society, colon cancer is the third most common cancer in the U.S. in both men and women, with more than 93,000 cases diagnosed in 2015.

Researchers have long known that blacks develop colon cancer at an earlier age and that blacks with colon cancer are at higher risk of dying of the disease than are whites. However, it has been difficult to identify why the differences in survival exist.

Researchers analyzed data from a large clinical trial of more than 3,000 patients with stage III colon cancer. The analysis revealed that tumors from whites, blacks and Asians had different frequencies of mutations in two key cancer-related genes, BRAF and KRAS, which have been associated with worse outcomes. It also found that colon cancers were twice as likely to recur in black patients as in whites; however, the discrepancy was only evident in those younger than age 50.

Some of the potential reasons for this disparity include socio-economic factors, such as diagnosis at a later stage, decreased access to health care and suboptimal treatment.

"The role of the biology of colon tumors according to race has not been examined as extensively," Dr. Yoon said. "This biology can be reflected in the genetic makeup of tumors, as well as by whether and how quickly cancer returns after the patient has been treated."

Dr. Yoon and his colleagues focused their efforts on finding out if colon cancers are genetically different based on race, and if race-based differences exist in recurrence rates. To do this, they examined data from the Alliance N0147 clinical trial, which included patients with stage III colon cancer from many centers in North America who all underwent surgery to remove their cancer and received chemotherapy after surgery.

As part of the trial, the patients provided a self-description of their race as white, Asian, or black or African-American. The researchers then evaluated the tumors from these participants to see if a mutation was present in the cancer-related genes BRAF and KRAS. They also noted if the cancer had returned after treatment.

The data showed that tumors from whites, blacks and Asians were different in terms of the frequency of mutations in the BRAF and KRAS genes. Tumors from whites were twice as likely to have BRAF mutations, whereas, tumors from blacks had the highest frequency of KRAS mutations. Tumors from Asians were the most likely to have normal copies of both genes.

The analysis also indicated that blacks had more than double the risk of cancer recurrence, compared with whites. However, this discrepancy was only visible among young patients — those younger than 50. Almost half of younger black patients experienced colon cancer recurrence within five years, compared with only 22 to 35 percent of white or Asian patients of any age.