Anaplastic thyroid carcinoma accompanied by uncontrollable eosinophilia.

: Anaplastic thyroid carcinoma is a rare disease, and cases associated with eosinophilia are even rarer. We herein report a case of anaplastic thyroid carcinoma accompanied by remarkable and uncontrollable eosinophilia. A 71-year-old man was diagnosed with end-stage anaplastic thyroid carcinoma. Throughout the aggressive clinical course of the cancer, eosinophilia dramatically progressed and became extremely refractory to steroid treatment. We measured the serum levels of hematopoietic cytokines potentially involved in eosinophilia, including granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-3 and IL-5. Although the GM-CSF level was moderately elevated, both the IL-3 and IL-5 levels were within the normal ranges. In this case, the patient's eosinophilia may have been related to his severe dyspnea and was likely responsible for the allergic reaction to the anticancer drug. Therefore, it is essential to elucidate the etiology of eosinophilia in patients with thyroid cancer in order to improve the treatment for patients with anaplastic thyroid carcinoma.