A Multicenter, Randomized, Double-Blind, Placebo-Controlled, Phase 3 Trial of Lenvatinib (E7080) in 131I-Refractory Differentiated Thyroid Cancer

Randomization Phase: Participants will receive blinded study drug (lenvatinib/placebo) in 2:1 ratio until documentation of disease progression (confirmed by independent imaging review), development of unacceptable toxicity, or withdrawal of consent. After having completed the primary analysis, subjects treated with lenvatinib who have not experienced disease progression may request to continue open label lenvatinib at the same dose, according to the clinical judgment of the investigator. Participants who discontinue treatment for any reason other than disease progression will be followed in the Randomization Phase until disease progression or start of another anticancer treatment; these participants then enter the Extension Phase for survival follow-up. Extension Phase: Participants in the placebo arm who have disease progression confirmed by IIR could request to enter the OOL Lenvatinib Treatment Period and receive lenvatinib treatment. Participants will receive lenvatinib treatment until disease progression (investigator's assessment), development of intolerable toxicity, or withdrawal of consent. Participants who had disease progression during the Randomization Phase and did not enter the OOL Lenvatinib Treatment Period and all participants who discontinued lenvatinib treatment in the OOL Lenvatinib Treatment Period will enter the follow-up period. Participants will be followed for survival, and all anticancer treatments will be recorded until the time of death.