May 25, 2016 by NCI Staff
African Americans who are diagnosed with colorectal cancer at a young age have significantly worse survival rates than young white patients, according to a new study.
The disparity was found even among those who were diagnosed with early-stage disease, Elena Stoffel, M.D., of the University of Michigan Comprehensive Cancer Center, and her colleagues reported May 2 in the Journal of Clinical Oncology.
With the advent of guidelines recommending routine screening for colorectal cancer starting at age 50 and advances in treatment, the overall rates of colorectal cancer incidence and mortality among individuals aged 50 years or older have declined over the last decade. Despite this progress, racial/ethnic disparities in colorectal cancer continue to exist. Colorectal cancer incidence and mortality are highest among African Americans compared with other racial/ethnic groups, and African American 5-year survival rates are the lowest.
In people younger than age 50, colorectal cancer incidence has risen by 1.5% annually since 1992 for reasons that are not fully understood. Among African Americans specifically, young-onset colorectal cancer is nearly twice as common as it is among whites. In the new study, the research team wanted to see whether the survival disparity observed for older African Americans with colorectal cancer also extended to younger patients.
“We hypothesized that the colorectal tumors that occur in young people may take a more aggressive course,” Dr. Stoffel said.
There is preliminary evidence that colorectal tumors in African Americans are more likely to have molecular characteristics associated with worse outcomes than those in whites and Hispanics, the researchers wrote. These include mutations in the KRAS gene and changes that affect a cell’s ability to repair errors made during DNA replication (i.e., defective DNA mismatch repair).
Using data from NCI’s Surveillance, Epidemiology, and End Results (SEER) program, the researchers identified 28,145 individuals between the ages of 20 and 49 who had been diagnosed with colorectal cancer during the 10-year period from 2000 through 2009.
By limiting the study population to individuals younger than the recommended age at which routine screening often begins, the study removed screening as a variable that could produce disparities, Dr. Stoffel explained.
The researchers found that young African Americans fared significantly worse in terms of 5-year survival at every stage of disease compared with white and Hispanic patients. The greatest disparities were among young African Americans with stage II or stage III cancers. Young African Americans with stage II disease, for example, had a 60%–70% higher risk of death due to colorectal cancer compared with young white patients with stage II disease. This finding differs from previous studies, which showed the most pronounced racial disparities in survival were among those with advanced-stage disease.
“We were very interested in this last finding because patients with stage II colorectal cancer typically have good prognoses when treated with surgery alone,” said Dr. Stoffel.
Adjuvant chemotherapy has been shown in several clinical trials to have minimal or no benefit in stage II disease. However, those results derive from studies mostly of patients diagnosed at an older age, Dr. Stoffel said.
“It’s unclear what factors are responsible for the current findings, especially given the fact that we had only SEER data to work with,” said Dr. Stoffel. “However, the fact that we’re seeing a big disparity in outcomes in young blacks with stage II disease suggests that early-stage tumors may behave differently in young-onset patients and, in particular, in young-onset black patients.
“Could it be due to differences in tumor biology, to differences in treatments that were offered, or to some sort of interactive response between tumor and treatment?” she continued. “In the end, we’re left with a lot of questions that only more research can answer.”
Despite many unanswered questions, the current study clearly demonstrates the need for more research to further our basic and clinical understanding of cancer in younger populations, said Nita Seibel, M.D., of NCI’s Division of Cancer Treatment and Diagnosis.
“Relatively few molecular genetic studies of colorectal cancer have been conducted in this age group,” added Dr. Seibel.
“The study highlights the importance of obtaining more biospecimens and conducting basic, biologic, genomic, and translational research to determine whether young-onset colon cancer tumors are molecularly different from older-onset cancers,” she continued. “Once more studies are completed, we will be in a better position to evaluate and inform screening, treatment, and prevention practices.”