Osimertinib is a standard treatment for epidermal growth factor receptor (EGFR)-mutated, T790M-positive patients with progression during EGFR-tyrosine kinase inhibitor (TKI) therapy. Osimertinib, a third-generation EGFR-TKI, allows progression-free survival of around 10 months, but its toxicity is well-tolerated compared with other EGFR-TKIs. Preclinical and clinical evidence suggests that EGFR-TKI may work synergistically with vascular endothelial growth factor inhibitors. We therefore plan a phase I/II study to investigate this possibility. In phase I, the primary endpoint is assessment of the tolerability of osimertinib and bevacizumab in 6 patients. Phase II then explores the efficacy of combined treatment compared with osimertinib monotherapy with progression-free survival as the primary endpoint. Secondary endpoints are overall response rate, time to treatment failure, overall survival, and safety. Eighty patients will be enrolled in phase II.