Lenvatinib for unresectable anaplastic thyroid cancer: real-world experiences in multi-institutional study

Purpose: Anaplastic thyroid carcinoma (ATC) is a rare, aggressive malignancy with poor prognosis. Lenvatinib has demonstrated moderate efficacy and is approved for unresectable ATC treatment in Japan. However, some patients are unable to tolerate the standard 24 mg daily dose and require dose reductions or interruptions due to its high incidence of adverse effects. This study aimed to evaluate the therapeutic effects of lenvatinib in patients with ATC, particularly assessing outcomes with reduced dosages across multiple institutions. Methods: Sixteen patients diagnosed with ATC and treated with lenvatinib were evaluated retrospectively. Overall survival (OS) and progression-free survival (PFS) were calculated. In addition, patients were divided into two groups based on 24 mg daily dose or reduced initial dose, and their therapeutic outcomes were compared. Results: The objective response rate was 31%, and the median OS and PFS were 2.2 and 1.7 months, respectively. Among the 16 patients, 11 (69%) initiated treatment with 24 mg daily, while the remaining 5 (31%) received a reduced dose. The median OS and PFS were 2.0 months and 1.4 months, respectively, among patients in the 24 mg daily group, compared to 6.2 months and 2.4 months, respectively, among patients in the reduced dosage group. Conclusion: Our study demonstrated that lenvatinib has moderate efficacy for ATC. In addition, initiating treatment at a reduced dose could provide therapeutic benefit. Lenvatinib may serve as a treatment option for unresectable ATC when targeted therapies, including BRAF, RET, and NTRK inhibitors, are unavailable. Furthermore, although the standard 24 mg daily dose is recommended, a lower initial dosage may be effective for patients unable to tolerate the full dose.