Clinical outcomes in patients with radioiodine refractory thyroid carcinoma treated with dose-reduced lenvatinib

e18104 Background: In recent years, well-differentiated thyroid cancer (WDTC) accounted for over 40,000 new cancer diagnoses annually. For patients with metastatic, iodine-131-refractory thyroid cancer, systemic therapy is sometimes warranted. Lenvatinib was FDA approved in this setting at a starting dose of 24 mg orally daily based on the SELECT trial. Many patients required dose reductions on this trial, and the use of full dose (24 mg) lenvatinib is often not feasible in clinical practice. This study characterizes the clinical outcomes of lenvatinib for WDTC in a real-world setting. Methods: This study is a retrospective chart review of all patients over 18 years old diagnosed with radioiodine refractory thyroid carcinoma who received lenvatinib at a large academic center between 05/01/2016 and 01/01/2022. Demographic information, clinical data, and treatment outcomes were obtained. Results of our study were compared to historical controls from the SELECT trial. Results: There were 38 patients included in this study. Twenty-six of 38 patients had a dose reduction prior to start of treatment per judgement of the treating physician. Of the 12 patients who started at 24 mg, 11 required a dose reduction. Starting doses of lenvatinib ranged from 4 mg to 24 mg. The mean starting dose was 17 mg. Median progression free survival and overall survival were 35.2 months and 56.2 months, respectively. Eighteen patients remain on therapy. Overall response rate was 39.5% compared to 64.8% in historical controls. Disease control rate was 63.2%. Any grade weight loss was higher in this cohort versus historical control – 92.1% vs 46.4%, respectively. Systolic ( > 20 mmHg) and diastolic ( > 10 mmHg) blood pressure changes occurred in 13.2% of patients. 16.7% of patients had a peak increase in creatinine > 0.2 mg/dL above their baseline. Conclusions: Many patients were deemed ineligible for full dose lenvatinib by the treating physician. Despite an apparently lower response rate, lower doses of lenvatinib can still provide adequate disease control with an acceptable rate of blood pressure and serum creatinine elevation. Weight loss was an almost universal side effect of lenvatinib in this real-world population and was seen at a higher frequency than the historical population.