The INSR exists as two splice variant isoforms: the INSR-B isoform that is responsible for signaling metabolic responses involved mainly in the regulation of glucose uptake and metabolism and the INSR-A isoform that is expressed in certain tumours (such as mammary cancers), signals predominantly mitogenic responses, and is capable of binding IGF-II with high affinity [20, 21]. This evidence concerns the gene INSR and breast cancer.