Characterization of Tumor Size Changes Over Time From the Phase 3 Study of Lenvatinib in Thyroid Cancer

<jats:sec> <jats:title>Context:</jats:title> <jats:p>Lenvatinib improved the progression-free survival (PFS) and overall response rate of patients with radioiodine-refractory differentiated thyroid cancer vs placebo in the Phase 3 Study of (E7080) Lenvatinib in Differentiated Cancer of the Thyroid (SELECT).</jats:p> </jats:sec> <jats:sec> <jats:title>Objective:</jats:title> <jats:p>The objective of the study was to characterize tumor size changes with lenvatinib treatment.</jats:p> </jats:sec> <jats:sec> <jats:title>Design:</jats:title> <jats:p>SELECT was a phase 3, randomized, double-blind, multicenter study.</jats:p> </jats:sec> <jats:sec> <jats:title>Setting:</jats:title> <jats:p>In this clinical trial, tumor assessments of lenvatinib (n = 261) and placebo-treated (n = 131) patients were performed by independent radiological review per Response Evaluation Criteria in Solid Tumors version, 1.1 at 8-week intervals.</jats:p> </jats:sec> <jats:sec> <jats:title>Patients:</jats:title> <jats:p>Patients with complete or partial response were defined as responders to lenvatinib (n = 169). Of the 92 nonresponders, 76 had at least one postbaseline tumor assessment and were included in this analysis.</jats:p> </jats:sec> <jats:sec> <jats:title>Interventions:</jats:title> <jats:p>Lenvatinib (24 mg once daily) or placebo in 28-day cycles until unacceptable toxicity, disease progression, or death.</jats:p> </jats:sec> <jats:sec> <jats:title>Main Outcome Measures:</jats:title> <jats:p>This was an exploratory analysis of key end points from SELECT, including PFS, overall response rate, and tumor reduction.</jats:p> </jats:sec> <jats:sec> <jats:title>Results:</jats:title> <jats:p>The median maximum percentage change in tumor size was −42.9% for patients receiving lenvatinib (responders, −51.9%; nonresponders, −20.2%). Tumor size reduction was most pronounced at first assessment (median, −24.7% at 8 wk after randomization); thereafter, the rate of change was slower but continuous (−1.3% per mo). In a multivariate model, percentage change in tumor size at the first assessment was a marginally significant positive predictor for PFS (P = .06).</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusions:</jats:title> <jats:p>The change in tumor size conferred by lenvatinib was characterized by two phases: an initial, rapid decline, followed by slower, continuous shrinkage.</jats:p> </jats:sec>