Kaiser Permanente study also identifies survival differences among Asian American ethnic groups, highlighting importance of looking at variations within this community
Personal and lifestyle factors — such as body mass index and smoking history — may help explain why many studies have found breast cancer survival rates to be higher in Asian American women than other women in the U.S., new Kaiser Permanente research suggests.
The study, published in the Journal of the National Cancer Institute, compared overall survival and breast cancer-specific survival in 5,294 Asian American women and 5,294 non-Latina White women diagnosed with breast cancer between 2000 and 2015 at Kaiser Permanente Northern California (KPNC).
The new study, like prior studies, found that Asian American women had improved overall survival and breast cancer-specific survival. Specifically, by 2020, there were 1,048 deaths among the Asian American women, with 581 due to breast cancer, and 1,673 deaths among the White women, with 779 due to breast cancer.
However, in addition to comparing Asian American women to White women, the research team also looked at differences within the ethnic groups that make up the broader Asian American community. These analyses found a clear survival advantage for Chinese, Japanese, and South Asian women compared to White women.
“To our knowledge, this is the first comprehensive study investigating the apparent survival advantage between Asian American women and White women with breast cancer that was also able to look at specific Asian American ethnicities,” said lead author Marilyn L. Kwan, PhD, a research scientist at the Kaiser Permanente Division of Research (DOR). “We showed that the survival advantage is true for Chinese, Japanese, and South Asian women. For the other ethnic groups, the findings were more nuanced.”
Because the study focused on KPNC members, the research team was able to rule out health care access factors that can contribute to survival differences. “Everyone in our study had health insurance, and we know lack of access to health care is a factor in cancer outcomes,” said senior author Lawrence H. Kushi, ScD, a DOR research scientist. “Also, everyone had access to the same high-quality care. This created a setting where we could look at an array of other factors that might contribute to the survival advantage.”
Personal, social, and cultural factors
Asian Americans are a diverse, rapidly growing population, comprising people from 30 different countries, speaking more than 100 different languages and dialects. The large and diverse Asian American community in Northern California — and at Kaiser Permanente specifically — also made it possible for the researchers to perform unique group analyses. Within the Asian American group, 27.3% of the women were Chinese, 40.5% were Filipina, 8.5% were Japanese, 2.8% were Korean, 8.6% were South Asian, 5.1% were Southeast Asian, and 7.1% had more than one Asian ethnicity.
These specific analyses differed from many prior studies because they accounted not only for tumor type, treatment, smoking, and body mass index, but also the potential influence of specific social, cultural, or environmental factors. For this part of the analysis, address was used to assess 4 aspects of their neighborhood environment: socioeconomic status, percent of Asians in the neighborhood, percent of foreign-born Asians or households with limited English speakers; and percent of businesses that promote Asian cultural and social identities.
The study found that after accounting for BMI and smoking, survival differences narrowed. The researchers say this suggests lifestyle factors may be more significant than social and environmental factors in explaining why Asian American women have better breast cancer survival. But they also noted that smoking and body mass index could not explain the full survival advantage.
“This indicates that there are other factors as yet unaccounted for and that warrant further investigation,” said co-author Scarlett Lin Gomez, PhD, MPH, an epidemiologist at the University of California, San Francisco. “But it also reinforces that refraining from or quitting smoking and maintaining a lower weight are important contributors to survival after a breast cancer diagnosis.”
This new study is part of a larger research project investigating the improved survival seen in Asian American cancer survivors being conducted with researchers not only at UCSF and Kaiser Permanente, but also at the Roswell Park Comprehensive Cancer Center, Stanford University, the University of Hawaii, and the University of Southern California. The larger study will analyze social and treatment factors, tumor genomics, and treatment factors that might influence survival in 4 groups of breast cancer survivors, including those at KPNC.
“We often focus our research efforts on identifying factors contributing to poorer outcomes among certain population groups, and, while this is important, shifting this paradigm to study factors contributing to more favorable outcomes after a cancer diagnosis can provide valuable insights into identifying factors that may help us to improve outcomes for all population groups,” said Gomez.
Added Kwan: “What we learn from Asian American breast cancer survivors can benefit all women and men with breast cancer.”
This study was supported by the National Cancer Institute.
Co-authors include Lia D’Addario, MPH, Janise Roh, MSW, MPH, Isaac J. Ergas, PhD, MPH, MFA, of the Division of Research; Catherine Lee, PhD, Salma Shariff-Marco, PhD, MPH, Iona Cheng, PhD, MPH, Julie Von Behren, MPH, Esperanza Castillo, MS, Mi-Ok Kim, PhD, and Katherine Lin, MPH, of the University of California, San Francisco; Anna H. Wu, PhD, of the University of Southern California; Brittany N. Morey, PhD, MPH, of the University of California, Irvine; Lenora WM Loo, PhD, University of Hawaii Cancer Center; Allison Kurian, MD, MSc, and Esther M. John, PhD, MSPH, of Stanford University School of Medicine; and Angela R. Omilian, PhD, and Song Yao, MD, PhD, of the Roswell Park Comprehensive Cancer Center.
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About the Kaiser Permanente Division of Research
The Kaiser Permanente Division of Research conducts, publishes, and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. KPDOR seeks to understand the determinants of illness and well-being and to improve the quality and cost-effectiveness of health care. Currently, DOR’s 720-plus staff, including 73 research and staff scientists, are working on nearly 630 epidemiological and health services research projects. For more information, visit divisionofresearch.kp.org.
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