However, several observations suggest that IGF-IR may be required for maintaining the transformed state: IGF-IR is required for the transformation of fibroblasts by SV40 [57], it is able to improve the efficiency of EGFR signaling in tamoxifen-resistant cells [52], and its inhibition enhances the inhibitory effects of gefitinib in breast cancer cells [58]. Here, IGF1R is linked to breast cancer.