Insulin receptor (IR) and the type I IGF receptor (IGF1R) are structurally and functionally related. The function of IGF1R in cancer has been well documented and anti-IGF1R strategies to treat cancer have shown initial positive results. However, the role of IR in tumor biology, independent of IGF1R, is less clear. To address this issue, short hairpin RNA (shRNA) was used to specifically downregulate IR in two cancer cell lines, LCC6 and T47D. Cells with reduced IR showed reduced insulin-stimulated Akt activation, without affecting IGF1R activation. Cells with reduced IR formed fewer colonies in anchorage-independent conditions. LCC6 IR shRNA xenograft tumors in mice had reduced growth, angiogenesis and lymphangiogensis when compared with LCC6 wild-type cells. Accordingly, LCC6 IR shRNA clones produced less hypoxia-inducible factor-1alpha, vascular endothelial growth factor (VEGF)-A and VEGF-D. Furthermore, LCC6 IR shRNA cells formed fewer pulmonary metastases when compared with LCC6 wild-type cells. Using in vivo luciferase imaging, we have shown that LCC6 IR shRNA cells have less seeding and colonization potential in the lung and liver of mice than LCC6 cells. In conclusion, downregulation of IR inhibited cancer cell proliferation, angiogenesis, lymphangiogenesis and metastasis. Our data argue that IR should also be targeted in cancer therapy.