Patients with radioiodine-refractory differentiated thyroid cancer (RAI-R DTC) with BRAF V600E and/or K601E mutation status: A real-world view of effectiveness of lenvatinib monotherapy.

6098 Background: Lenvatinib was approved for the treatment of patients RAI-R DTC in the United States (US) in 2015, and the treatment landscape has evolved with agents targeting specific driver mutations. We assessed real-world clinical effectiveness of first line therapy with lenvatinib in patients with BRAF-mutated tumors, wild-type (WT) tumors, and patients who have not been tested for BRAF mutations (BRAF untested tumors). Methods: A retrospective chart review of RAI-R DTC patients in the US who initiated first-line lenvatinib monotherapy between February 13, 2015, and September 30, 2020. Data, including a boosted cohort of patients with BRAF-mutated tumors collected in late 2023, were abstracted from patients’ electronic health records and were de-identified. Descriptive analyses were conducted in patient cohorts with BRAF V600E and/or K601E mutated tumors, wild-type (WT) tumors, and BRAF untested tumors. Best response in first-line therapy was captured, real-world progression-free survival (rwPFS) and real-world overall survival (rwOS) were assessed using Kaplan-Meier methods. Results: Of the 361 patients reviewed, 185 had records showing BRAF mutational status testing. 89 had BRAF V600E and/or K601E mutated tumors, 96 had WT tumors. 176 patients did not have BRAF mutational assessment. Of all subjects, 73.7% were White/Caucasian, 15.2% were African American, and 16.8% were Hispanic/Latino; 27.1% had ECOG performance status ≥2. The median follow-up times for each cohort were 30.0, 18.7 and 18.0 months, showing the longer follow up period for the BRAF-mutated cohort boost. Kaplan-Meier estimation for lenvatinib treatment discontinuation for the three cohorts at 24-months were as shown in the table below. Provider-reported overall response rate (complete or partial response) was 76.4%, 75.0% and 69.3% respectively. The estimated 24-month rwPFS rates (95% CI) were 74.1% (62.2%-82.8%), 61.7% (49.6%-71.8%), and 69.8% (60.9%-77.0%) respectively. Median rwOS was not reached for patients with BRAF-mutated and WT tumors, median OS was 54.2 months for BRAF untested tumors. Estimated rwOS rates at 12- and 48-months were 93.2% (85.4%-96.9%) and 83.9% (73.3%-90.3%) in BRAF-mutated patients, 90.6% (82.8%-95.0%) and 68.5% (53.4%-79.6%) in WT patients, and 90.2% (84.7%-93.8%) and 72.5% (61.6%-80.7%) in BRAF untested patients respectively. Conclusions: In this US real-world experience, the effectiveness of lenvatinib is consistent across a diverse cohort of RAI-R DTC patients with BRAF-mutated, WT, and BRAF untested tumors. This has implications for the first-line use of lenvatinib in BRAF mutated patients. Table: see text