Lower breast cancer risk among women with two Hakka parents in Taiwan: A nationwide population-based study

BACKGROUND: Breast cancer is the most common cancer among women in Taiwan, yet most epidemiological studies treat Taiwanese Han women as a homogeneous population. Whether breast cancer occurrence differs across major Han subgroups, such as Hakka and Min-nan, remains insufficiently explored. METHODS: We conducted a nationwide, population-based study by linking the Taiwan Biobank (TWB) with the National Cancer Registry (NCR) and the National Health Insurance Research Database (NHIRD). A total of 78,530 women aged 30-70 years were included, comprising 879 breast cancer cases and 77,651 controls. Parental ethnic/dialect background was determined by the self-reported ethnicity of both parents and categorized as Min-nan, Hakka, or Mainland Chinese. Multivariable logistic regression models were used to estimate adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for breast cancer risk associated with parental ethnicity, adjusting for demographic characteristics, lifestyle behaviors, reproductive factors, family history of breast cancer, and metabolic comorbidities. RESULTS: After multivariable adjustment, women with two Hakka parents had a significantly lower odds of breast cancer compared with those with two Min-nan parents (aOR, 0.75; 95% CI, 0.60-0.95). No significant associations were observed for other parental ethnic combinations. Advancing age was strongly associated with increased breast cancer risk, as was diabetes mellitus (aOR, 1.28; 95% CI, 1.07-1.52). A family history of breast cancer in first-degree relatives, including mothers and sisters, was also independently associated with higher odds. Lifestyle factors, anthropometric measures, and reproductive variables showed no significant associations after adjustment. CONCLUSIONS: In this nationwide cohort, breast cancer occurrence differed within the Taiwanese Han population, with a lower risk observed among women with Hakka ancestry on both parental sides. These findings highlight meaningful within-population heterogeneity and underscore the importance of considering ethnic and cultural subgroups in breast cancer epidemiology and risk stratification.