Impact of baseline tumor burden on overall survival in patients with radioiodine‐refractory differentiated thyroid cancer treated with lenvatinib in the SELECT global phase 3 trial

BACKGROUND: Radioiodine‐refractory differentiated thyroid cancer (RAI‐R DTC) is an aggressive form of thyroid cancer. Lenvatinib is a multikinase inhibitor approved for treatment of RAI‐R DTC. The impact of tumor response and tumor burden on overall survival (OS) after lenvatinib treatment in patients with RAI‐R DTC was assessed. METHODS: Data from patients treated with lenvatinib (N = 261) in SELECT were retrospectively analyzed. Patients were divided into lenvatinib responder or nonresponder subgroups and into low (≤40 mm) or high (>40 mm) tumor burden subgroups based on baseline sums of diameters of target lesions using Response Evaluation Criteria in Solid Tumors, version 1.1 (cutoff values were determined by receiver‐operating characteristic analyses). Associations of tumor response and tumor burden with OS were assessed. RESULTS: Median OS was prolonged in lenvatinib responders versus nonresponders (52.2 vs 19.0 months; hazard ratio [HR], 0.32; 95% CI, 0.23‐0.46). Patients with a lower tumor burden who received lenvatinib had prolonged OS versus those with a higher tumor burden (median OS, not reached vs 29.1 months, respectively; HR, 0.42; 95% CI, 0.28‐0.63). Baseline tumor burden was associated with OS by multivariate analysis (HR, 0.56; 95% CI, 0.35‐0.89; P = .0138). CONCLUSIONS: Patients with a lower tumor burden receiving lenvatinib had prolonged OS compared with those with a higher tumor burden receiving lenvatinib. Baseline tumor burden may be a prognostic factor for OS in patients with RAI‐R DTC treated with lenvatinib.