IRS1 and breast carcinoma: Besides its conventional role, IRS-1 has been found in the nuclear compartment in several cell types, including breast cancer cells and breast tumors [32, 33], where it functions as transcriptional coregulator for RNA polymerases I and II [34]. In vivo transgenic mouse models of breast cancer showed that loss of IRS-1 enhances breast cancer metastasis, supporting the hypothesis that IRS-1 may have a metastasis suppressor function [35].