Inhibiting MEK can resensitize tumours to sunitinib in a patient-derived xenograft mouse model of renal cell carcinoma. Tumours in mice treated with sunitinib alone developed resistance to therapy after 30 days, whereas mice treated with either sunitinib in combination with the MEK inhibitor PD-325901 or that received PD-325901 after the onset of resistance to sunitinib continued to have a tumour response.