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USC researchers examine cancer incidence

Lihua Liu, assistant professor of clinical preventive medicine at the Keck School of Medicine of USC
Lihua Liu, assistant professor of clinical preventive medicine at the Keck School of Medicine of USC

Based on a comprehensive study that included more than half the Asian-American and Native Hawaiian and Other Pacific Islander (NHOPI) populations, a team of scientists led by members of the Keck School of Medicine of USC and the Cancer Prevention Institute of California (CPIC) has produced the first analysis of national trends in cancer incidence among 11 Asian-American and NHOPI groups.

The researchers examined population-based cancer incidence rates and trends from 1990 through 2008, using data collected by 13 registries of the National Cancer Institute’s Surveillance, Epidemiology and End Results (SEER) program.

The groups studied in detail included Asian-Indians/Pakistanis, Chinese, Filipinos, Guamanians/Chamorros, Japanese, Kampucheans (Cambodians), Koreans, Laotians, Native Hawaiians, Samoans and Vietnamese, representing 54 percent of all Asian-Americans and 65 percent of all NHOPIs in the United States. The studies, which appeared in a pair of articles published online in the Journal of the National Cancer Institute, revealed substantial disparities and complexities in cancer incidence patterns and trends among these population groups.

“Most importantly, these studies examine the cancer burden in each of these individual groups instead of lumping them into a single category as they often are,” said Lihua Liu, assistant professor of clinical preventive medicine at the Keck School and lead author of the NHOPI analysis. “These population groups are so different from each other, in terms of culture, language, history, socioeconomic status and risk exposures. Putting them all into one group masks the unique cancer patterns and experiences of each subgroup, so the results do not accurately represent any one of the groups.”

Though previous studies had reported regional cancer incidence patterns and trends among Asian-American subgroups, no national data were available, and little was known about the differences among NHOPI populations. The SEER registries formed a work group to bridge that knowledge gap by developing annual population estimates classified by detailed racial/ethnic scheme.

As one of the SEER registries, the Los Angeles Cancer Surveillance program, administered within the Department of Preventive Medicine at USC, participated in the study. Dennis Deapen, director of the Los Angeles surveillance program and professor of preventive medicine at the Keck School, also was a co-author on both articles.

Though the NHOPIs represent 0.4 percent of the total U.S. population, their population growth rate is three times faster than that of the country’s total population. In their article, Liu and colleagues reported clear differences in cancer incidence rates among NHOPI subgroups and between NHOPIs and non-Hispanic whites by cancer type. For example, breast cancer incidence rates decreased by 4.1 percent a year among Native Hawaiian women after 1998, but they increased at an annual rate of 2.7 percent among Samoan and Guamanian women. Though the NHOPI subgroups shared the similar pattern of top common cancers, including prostate, breast, lung and colorectal as non-Hispanic whites, they also have higher incidence rates of stomach, liver and uterus cancers compared to non-Hispanic whites.

“One of our most unique observations is the seemingly migrant effect on cancer risk of the Native Hawaiians,” Liu said. “For the first time, we report geographic differences in cancer rates for this population. Their change in cancer risk is similar to what we see in immigrants who come from other countries, which strongly indicates the environmental influence on cancer incidence.”

Native Hawaiians living in Hawaii experienced higher risks for lung, breast and uterine cancers, but lower risks for colorectal and prostate cancers, compared to the Native Hawaiians living on the U.S. mainland. Liu said that future research designed to understand the causes for the geographic differences could help reduce cancer disparities among Native Hawaiians.

The Asian-American study, led by CPIC Research Scientist Scarlett Lin Gomez, found that prostate cancer was the most common type found among men, followed by lung, colorectal, liver and stomach cancer. When looked at individually, however, important differences arise. For example, lung cancer rates were highest among Kampuchean, Laotian and Vietnamese. Liver cancer continued to increase in Filipino, Kampuchean and Vietnamese men, in recent years surpassing lung cancer among Kampucheans.

And while breast cancer was the most common form of cancer among women, not all groups experienced the same incidence or trends over the study period. Chinese women, for example, experienced a greater than 1 percent increase annually in breast cancer rates throughout the nearly 20-year period. At the same time, Japanese women experienced an even greater annual increase (2.7 percent) between 1990 and 1998, but then a nearly 2 percent annual decrease after that.

Among men and women, in contrast to national declines in lung and colorectal cancer, the incidence of lung cancer has been increasing among Filipina and Korean women and Asian Indian/Pakistani men, and the incidence of colorectal cancer has been increasing among Kampuchean, Korean, and Laotian men and women.

These data fill a critical knowledge gap concerning the cancer experience of Asian-American and NHOPI populations and highlight where increased preventive, screening and surveillance efforts are needed.

The research was supported by the National Cancer Institute’s SEER program (grant number HHSN261201000035C) and the CPIC (grant number HHSN261201000140C).

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