Use of Insulin and Mortality from Breast Cancer among Taiwanese Women with Diabetes

Background. To evaluate whether insulin use was predictive for mortality from breast cancer in Taiwanese women with diabetes mellitus. Methods. A total of 48,880 diabetic women were followed up to determine the mortality from breast cancer during 1995–2006. Cox models were used, considering the following independent variables: age, sex, diabetes type, diabetes duration, body mass index, smoking, insulin use, and area of residence. Insulin use was also considered for its duration of use at cutoffs of 3 years and 5 years. Results. Age was a significant predictor in all analyses. The multivariable-adjusted hazard ratio (95% confidence interval, P value) for insulin use without considering the duration of use was not statistically significant (1.339 [0.782–2.293, P = 0.2878]). Compared with nonusers, insulin users showed the following adjusted hazard ratios for insulin use <3 years, ≥3 years, <5 years, and ≥5 years: 0.567 (0.179–1.791, P = 0.3333), 2.006 (1.102–3.653, P = 0.0228), 1.045 (0.505–2.162, P = 0.9048), and 1.899 (0.934–3.860, P = 0.0763). Conclusions. Insulin use (mainly human insulin) for ≥3 years may be associated with a higher risk of breast cancer mortality.