Prescription of Chinese herbal products is associated with a decreased risk of invasive breast cancer

The finding of a decrease in endometrial cancer incidence among breast cancer survivors following the use of Chinese herbal products (CHPs) has led to speculation that CHPs might play a role in breast cancer prevention. This study provides an overview of breast cancer incidence, comparing CHP users with those who do not use traditional Chinese medicine (TCM), referred to as non-TCM users. The results can provide information to clinicians for counseling women about the preventive use of TCM. A total of 184,386 women (20–79 years of age) were recruited from a nationwide 1-million-person representative sample of those covered by National Health Insurance in Taiwan and were followed from 1999 to 2012. A total of 1853 incidents of invasive breast cancer were diagnosed. The person-year approach with the Poisson assumption was used to estimate the incidence density rate. The age-specific hazard ratios of breast cancer in relation to either CHP or siwutang (SWT) use were calculated with multivariate Cox proportional hazard regression. More than 78% of patients had used a CHP at some point previously. The overall incidence density rate of breast cancer for non-TCM users was estimated at 1.73 per 10,000 patient-years. The corresponding values for CHP and SWT users were lower than those of the non-TCM group (CHP group = 0.85; SWT group = 0.63 per 10,000 patient-years). The covariate adjusted HRs for breast cancer were 0.57 (95% confidence interval [CI] 0.50–0.65) and 0.36 (95% CI 0.28–0.46) in women using CHPs and SWT, respectively. The findings were confirmed using propensity score matching. Consumption of CHPs reduces the incidence of invasive breast cancer. Although the mechanism of action of these products is unclear, their use as a preventive agent for breast cancer is appropriate for many women at an increased risk of breast cancer.