The association between exogenous insulin and cancer gained attention in 2009 when three observational studies evaluating cancer risks with different types of insulin were published concurrently [8]–[10], fuelling speculation of an increased risk of cancer (in particular breast cancer) associated with the insulin analogue insulin glargine, due to its higher affinity for the IGF-1 receptor in comparison with human insulin. This evidence concerns the gene INS and breast cancer.