INS and breast cancer: It is clearly demonstrated here that patients who had used only human insulin without the use of any other OAD might suffer from a significantly higher risk of breast cancer with an estimated hazard ratio of 1.413 (95 % confidence interval: 1.030-1.940), while those who had used OAD plus a short-term human insulin use of <2 years might have a significantly lower risk of breast cancer (Model I, Table 3).