This is a Phase 2, open-label, safety and activity study of lenvatinib in subjects with KIF5B-RET-positive adenocarcinoma of the lung and other confirmed RET translocations. At least 20 subjects with KIF5B-RET will be treated and will receive lenvatinib at a starting dose of 24 mg orally, once per day. Additional subjects with other RET translocations will be treated with lenvatinib at a starting dose of 24 mg orally, once per day. The study will consist of 3 phases: The Pretreatment Phase, The Treatment Phase and the Extension Phase. The Pretreatment Phase will include screening procedures and eligibility assessments. The Pretreatment Phase consists of a Screen 1, Screen 2 and Baseline Period. The Treatment Phase will begin when the subject has met all eligibility criteria on Day 1 of the first Treatment Cycle. The Treatment Phase contains the Treatment and Follow-up Periods. The Extension Phase will begin for subjects who received treatment in the study (either in the Treatment Period or Follow-up Period) at the time of database cutoff.