Secular trend for mortality from breast cancer and the association between diabetes and breast cancer in Taiwan between 1995 and 2006

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Abstract
Aims/hypothesis Studies have identified an association between diabetes and breast cancer in postmenopausal women in Western countries. Such an association needs to be confirmed in an Asian population. The aim of this study was to evaluate the secular trend for breast cancer mortality in Taiwanese women in the general population and the mortality rate ratios between diabetic patients and the general population. Methods Age-specific mortality rates for the general population, categorised into groups aged 25–54, 55–64, 65–74 and ≥75 years, were calculated for the years between 1995 and 2006 (inclusive) from vital statistics published by the Taiwanese government. Linear regression was used to test the trends. A total of 131,573 diabetic women aged ≥25 years from a national cohort recruited between 1995 and 1998 (inclusive) were followed prospectively for vital status, determined from the National Register of Deaths. Mortality rates and mortality rate ratios (mortality rate in diabetic women vs the average and highest mortality rates for the general population) were calculated. Results A total of 14,230 women aged ≥25 years in the general population died of breast cancer between 1995 and 2006. A trend for an increase in the annual rate was observed for all age groups. A total of 482 diabetic women died of breast cancer, with a crude mortality rate of 45.7 per 100,000 person-years. Compared with the general population the relative risk of mortality for those with diabetes ranged from 1.37 (for the group aged 55–64 years) to 2.43 (for the group aged 25–54 years). Conclusions/interpretation We identified a secular trend of an increase in the rate of breast cancer mortality in the Taiwanese general population. Our data suggest a higher risk of breast cancer mortality in diabetic patients in all age groups.