The genetic makeup of colon cancer tumors and survival rates for patients with the disease differ by race, according to a study published in the Journal of the National Cancer Institute (2015; doi:10.1093/jnci/djv186).
“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 Yoon, MD, an oncologist at the Mayo Clinic Cancer Center in Rochester, Minnesota. “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 both men and women, with an estimated more than 93,000 cases in 2015. Researchers have long known that blacks develop colon cancer at an earlier age and blacks with colon cancer are at higher risk of dying than whites. However, identifying why differences in survival exist has been difficult.
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 than in whites; however, the discrepancy was only evident in those younger than 50 years.
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,” said Yoon. “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.”
Yoon and his colleagues focused their efforts on finding out if colon cancers are genetically different based on race, as well as if race-based differences exist in recurrence rates. To do this, they examined data from a large clinical trial, Alliance N0147, which included patients with stage III colon cancer from many centers in North America who all underwent surgery to remove their cancer and chemotherapy after surgery.
As part of the trial, the patients provided a self-description of their race as either 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.
Analysis of 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.
“Because all patients were treated and had their disease monitored in a clinical trial,” said Yoon, “suboptimal treatment, differences in cancer stage, or reduced access to care cannot adequately explain the disparity.”