Anaplastic thyroid carcinoma (ATC), which accounts for 1%-2% of all malignant tumors of the thyroid, is known to be highly resistant to any therapy and has a 1-year survival rate of 5%-20% [1][2][3]. ATC patients are limited in number, and most die within 6 months after diagnosis, making it difficult to establish a standard treatment protocol. Multimodal therapy including surgery, radiotherapy and chemotherapy has been introduced, but survival times remain poor [4][5][6].The use of molecular-targeted drugs as cancer therapy has been rapidly increasing over the past decade. Lenvatinib, a new molecular-targeted anticancer drug, is a multi-targeted receptor tyrosine kinase inhibitor that inhibits the activities of vascular endothelial growth factor receptors, fibroblast growth factor receptors, platelet-derived growth factor receptors, KIT, and RET [7,8]. Lenvatinib exerts its anticancer activity via the suppression of tumor angiogenesis, and it is generally indicated for unresectable radioiodine-refractory differentiated thyroid cancers [9]. However, the evidence of the clinical effect of this drug on ATC is very limited. We herein report a case of ATC with local recur- Kurume Medical Journal, 64, 00-00, 2017 Summary: Objective: We report a case of anaplastic thyroid carcinoma (ATC) with local recurrence and distant metastasis that responded very well to treatment with lenvatinib, a new molecular-targeted anticancer drug. Case Report: A 91-year-old Japanese woman presented with a 5-month history of a painless mass in her left anterior neck. She had a past history of total thyroidectomy and neck dissection for papillary carcinoma of the thyroid. Here she underwent neck dissection, and the histopathological diagnosis was lymph node metastasis of papillary carcinoma with anaplastic transformation. Five months later, a cervical lymph node swelled up again.Computed tomography demonstrated an enhanced mass in the neck and multiple nodules in both lungs. Recurrent ATC with multiple lung metastases was diagnosed, and molecular-targeted therapy with lenvatinib was initiated. The neck tumor reduced in 1 week, and the pulmonary nodules became completely hollow within 1 month. However, we had to discontinue lenvatinib because of severe side effects including high blood pressure, hypocalcemia, and hypoalbuminemia. Soon after discontinuation, the side effects subsided, but the tumor rapidly regrew. The patient died of lymphangiosis carcinomatosa 6 days after discontinuation. Conclusion: Although recent advances in molecular-targeted therapy have provided powerful cancer therapy tools, the negative side of this therapy must be addressed.