Study ties lifestyle to higher breast cancer survival in Asian American women

Asian American women with breast cancer had higher survival rates than white women, though outcomes differed across ethnic groups within the population, according to new research.

The analysis from Kaiser Permanente included Chinese, Filipina, Japanese, Korean, South Asian and Southeast Asian patients diagnosed from 2000 to 2015 in Kaiser Permanente Northern California. Chinese, Japanese and South Asian women notably showed a consistent survival advantage, while other groups showed more variable results.

Researchers compared 5,294 Asian American women with 5,294 non-Latina white women with stage I to IV breast cancer and followed them through Dec. 31, 2020. They recorded 1,048 deaths among Asian American patients, including 581 from breast cancer, and 1,673 deaths among white patients, including 779 from breast cancer. Overall mortality remained lower among Asian American patients, with the clearest advantage among Chinese, Japanese and South Asian women.

Baseline differences between the groups included lower body mass index and lower smoking rates among Asian American patients. Median BMI was 24.8 compared with 27.4, and 47.2% of Asian American patients reported never smoking compared with 26.9% of white patients. After adjusting for BMI and smoking, survival differences narrowed, which Kaiser Permanente said suggested those factors accounted for part of the gap.

All patients received care within Kaiser Permanente Northern California, allowing researchers to examine outcomes within a single insured population. Senior author Lawrence H. Kushi said, “Everyone in our study had health insurance, and we know lack of access to health care is a factor in cancer outcomes. Also, everyone had access to the same high-quality care.”

Researchers also evaluated whether neighborhood conditions influenced survival. The analysis included socioeconomic status, the percentage of Asian residents, the proportion of foreign-born or limited-English-speaking households and the presence of businesses reflecting Asian cultural identity. Adjusting for these measures did not reduce survival differences to the same extent as BMI and smoking.

The patient population reflected wide variation across Asian ethnic groups. Filipina women made up 40.5% of the cohort, followed by Chinese at 27.3%, South Asian at 8.6%, Japanese at 8.5%, Southeast Asian at 5.1%, Korean at 2.8% and multiracial Asian at 7.1%. Separate national data show similar variation across Asian subgroups in cancer outcomes. A 2023 analysis from the Centers for Disease Control and Prevention found that late-stage breast cancer diagnoses ranged from 25.7% among Japanese women to 40.2% among women categorized as “Other Southeast Asian.”

Similar patterns have been documented in other areas of health care. Studies published in the Journal of the American College of Cardiology and the Journal of the American Heart Association found that aggregating Asian American patients into a single category obscured differences in heart failure care and pregnancy-related hypertension risk, which became visible only after data were analyzed by specific ethnic groups.