MON-521 An Open-Label, Single-Arm, Multicenter, Phase 2 Trial of Lenvatinib (LEN) for the Treatment of Anaplastic Thyroid Cancer (ATC)

Background: ATC is aggressive, with a low 5-year patient (pt)-survival rate. Apart from recent advances in treating ATCs in pts with BRAF mutations, systemic treatments have limited efficacy and duration of response is short. In a small, phase 2 study conducted in Japan, 24% of pts with ATC achieved a partial response (PR) with LEN (Study 208 [Takahashi, Future Oncol. 2019]). This study (NCT02657369 [Study 213]) aimed to further evaluate the efficacy and safety of LEN in a broader population of pts with ATC. Methods: Study 213 was performed in collaboration with the International Thyroid Oncology Group and enrolled pts with ATC to receive LEN 24 mg/day. Key inclusion criteria were: histologic diagnosis of ATC, measurable disease per RECIST v1.1, ECOG score ≤1, and adequate organ function. Previous surgery, radiation, and neoadjuvant, adjuvant, or palliative chemotherapy for ATC were allowed. The primary end point (confirmed objective response rate [ORR]) was determined by investigator review per RECIST v1.1. Interim analysis was done after the first 20 evaluable pts completed ≥2 tumor assessments (baseline and 6-week scan) or discontinued treatment. Results: The study was halted for futility when the minimum threshold for ORR (15%) was not met at the interim analysis. The full analysis set (FAS) included 34 pts because the protocol allowed enrollment until the interim analysis was complete. The median pt age was 66.5 years old and most were female (n=21/34), white (n=27/34), and had been treated with 1 or 2 prior anticancer regimens (n=20/34). Unconfirmed PR was experienced in 1/20 pts (ORR 5%; 95% CI 0.1–24.9%) in the interim analysis set. In the FAS, 1/34 pts had a confirmed PR (cPR) (ORR 3%; 95% CI 0.1–15.8%). In the interim and FAS, median progression-free survival (2.6 and 2.6 months, respectively) and median OS (2.9 and 3.2 months, respectively) were similar. In addition to the 1 cPR, 7 pts had 22–63% shrinkage in tumor measurements but did not meet the response criteria (FAS). Grade 3/4 treatment-emergent (TE) adverse events (AEs) occurred in 82.4% of pts, and 61.8% of pts experienced grade 3/4 treatment-related AEs (FAS). Grade 5 TEAEs occurred in 14/34 pts and there were 27 deaths by the time of data cut-off. There were no treatment-related deaths, and no major treatment-related bleeding events occurred. Conclusion: In contrast to Study 208, Study 213 enrolled more pts with ATC (34 vs 17), more of whom had received prior chemotherapy (62% vs 41%). Additionally, in Study 208, all pts were Japanese and tumor assessments were conducted more frequently (4- vs 6-weekly). These differences may have contributed to the observed variation in results between the 2 studies. AEs observed were consistent with the safety profile of LEN or with ATC. Further investigation of LEN in combination with a checkpoint inhibitor may be warranted.