Personal and lifestyle factors — such as body mass index and smoking history — may help explain why Asian American women have better breast cancer survival rates than other women in the U.S., a new Kaiser Permanente study suggests.
The research, published in the Journal of the National Cancer Institute, included 5,294 Asian American women and 5,294 non-Latina white women diagnosed with breast cancer between 2000 and 2015 at Kaiser Permanente in Northern California.
The new study, like prior studies, found that Asian American women lived longer. By 2020, there were 1,048 deaths among the Asian American women, with 581 deaths due to breast cancer, and 1,673 deaths among the white women, with 779 deaths due to breast cancer.
The research team also looked at differences among the ethnic groups that make up the broader Asian American community. This analysis 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 . “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 members of Kaiser Permanente Northern California, 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 everyone had access to the same high-quality care,” said senior author Lawrence H. Kushi, ScD, a research scientist. “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 comprise 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 — allowed the researchers to perform unique group analyses. Within the study’s 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.
The research looked at tumor type, treatment, smoking status, and body mass index as well as potential influence of specific social, cultural, or environmental factors. This included whether the women lived in a neighborhood with many other Asian individuals or in an area that included businesses that promoted Asian cultural and social identities.
The study found that after accounting for body mass index 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 fully explain the survival advantage, suggesting other unknown factors also play a role.
This study is part of a larger research project the investigators are conducting on Asian American cancer survivors. The larger study will analyze social and treatment factors, tumor genomics, and treatment factors that might influence survival.
“What we learn from Asian American breast cancer survivors can benefit all women and men with breast cancer,” said Kwan.
