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Tracking a discriminating killer

Researchers in Public Health Sciences Division expand understanding of how colorectal-cancer risks vary across racial, ethnic groups
Chloe Chien
Chloe Chien is a graduate student in the epidemiology program at the University of Washington and the lead author of a paper that breaks ground by evaluating the variation in colorectal-cancer risk across 18 different racial and ethnic subgroups. Study information may help reduce risk disparities. Photo by Todd McNaught

Colorectal cancer, one of the leading causes of cancer death in the United States, does not deal out suffering evenly.

Among patients diagnosed with the condition, people from certain racial and ethnic groups are at far greater risk than others of having advanced-stage cancer or of dying from their condition.

A study by researchers in the Public Health Sciences Division has found that the risks of both advanced-stage colorectal cancer and of death from the condition vary even more extensively with race than previously shown. The study, published in the August 1 issue of the journal Cancer, represents the most comprehensive analysis to date of a nationwide colorectal-cancer dataset sorted by race and ethnicity. It is also the first study to evaluate variation in risk across numerous racial and ethnic subgroups — information that could be useful for focusing future efforts to reduce risk disparities.

Knowledge of these disparities is not new. Previous studies showed a relationship between race/ethnicity and chances for early detection and survival. The American Cancer Society recognizes, for example, that African Americans have the highest death rate from colon cancer of any racial or ethnic group in the United States. Several studies have shown other racial and ethnic groups have similarly high risks of advanced-stage diagnosis and death when compared to non-Hispanic whites.

But the new study takes the analysis one step farther, evaluating the variation in risks across 18 different racial and ethnic subgroups. Using vast registries of public-access data from the nationwide Surveillance, Epidemiology and End Results (SEER) program, the researchers pinpointed particular subgroups with the highest and lowest risks.

Among the findings highlighted in the report were particularly strong variations within Asian and Hispanic categories.

"A lot of studies tend to lump all Asians and Pacific Islanders together and all Hispanics together," said Dr. Christopher Li, an assistant member in the Public Health Sciences Division and the senior author of the report. "But since Asian and Hispanic subgroups differ quite a bit with respect to their demographic characteristics, lifestyles, diets, etc., we had reason to think that they might also have important differences in their colorectal-cancer outcomes."

Specifically, the study showed (among other findings) that African Americans, American Indians, Chinese, Filipinos, Koreans, Hawaiians, Mexicans, South/Central Americans and Puerto Ricans were 10 to 60 percent more likely than non-Hispanic whites to be diagnosed with advanced-stage colorectal cancer. Meanwhile, Japanese Americans had a 20 percent lower risk. As for risk of mortality, African Americans, American Indians, Hawaiians, and Mexicans had a 20 to 30 percent greater risk than Caucasians while Chinese, Japanese, and Indians/Pakistanis had a 10 to 40 percent lower risk.

The authors noted that limited information about socioeconomic factors and other variables prevented a close analysis of what caused the differences in risks. However, based on other available evidence, they suggest that differences in socioeconomic status and access to health care likely account for a large share of the disparities they observed. Meanwhile, there is hope that some of the worst disparities could be reduced through targeted efforts to screen and treat underserved populations.

The continuing need to address the disease is apparent. Colorectal cancer, which develops in the lower digestive tract, accounts for roughly 11 percent of all cancer deaths, and is the second leading cause of cancer death in the United States, according to the American Cancer Society. An estimated 56,730 Americans died as a result of colorectal cancer in 2004.

And yet, effective screening techniques for colorectal cancer exist, and the survival rate can be up to 90 percent if colorectal cancers are caught at an early stage and treated effectively.

"Efforts to improve access to adequate health care for the populations we observed to be at greatest risk of poor colorectal-cancer outcomes may be an effective means of reducing these disparities," said Chloe Chien, graduate student in the epidemiology program at the University of Washington, and lead author on the paper.

Risks to Asians, Pacific Islanders

One example of how the study's subgroup analysis might help focus screening and treatment efforts is evident from their breakdown of risks to Asians and Pacific Islanders.

Overall, Li said, this group had no greater risk of advanced-stage colon cancer than non-Hispanic whites. But a closer analysis of the subgroups revealed new insights and showed some need for attention.

"We found that Japanese women actually had a lower risk of advanced-stage colon cancer compared to non-Hispanic white women, while other groups, such as Filipinos and Native Hawaiians had a higher risk," Li said.

Although the authors can only speculate about the reasons for higher risks in certain groups and subgroups, they indicate that multiple factors are probably involved. They also argue that genetic predisposition by race is unlikely, pointing to studies showing genetic variation to be even greater within a particular race than it is across races.

"I would say that the majority of the disparities we observed are due to socioeconomic factors and lifestyle factors rather than to genetic factors," Li said.

As a possible area for future research, Li hopes to look at how the disparities have changed over time. He suggests that recent efforts to educate the public and increase screening could help reduce the disparities between racial groups, but that they could also increase the gap if people acting on the information are those who already have access to health care resources.

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