INS and breast cancer: On the other hand, a lack of association with all-cancer mortality and all cancer other than breast cancer mortality regardless of the duration of insulin use, together with an increase in magnitude in the hazard ratios for breast cancer mortality among users of insulin for a longer duration (for ≥3 [or ≥5] years) (Table 3), support a specific link and probably a causal relationship between insulin use and breast cancer mortality.