Anatomopathological aspects of a malignant mixed thyroid tumor with multiple metastasis in a dog

Abstract

Thyroid tumors are uncommon. Malignant mixed tumor, or carcinosarcoma, is a rare, malignant, infiltrative, and metastatic neoplasm. This paper aims to report a case of a metastatic malignant mixed thyroid tumor in a 10-year-old mixed-breed female dog. The patient presented respiratory symptoms and had an unfavorable evolution of the clinical scenario. It was euthanized and submitted to necroscopic examination, which led to subsequent histopathological and immunohistochemical (IHC) evaluation. The macroscopic evaluation revealed neoformations in the thyroid, lung, heart, kidneys, and abdominal skeletal muscles. Microscopically, the thyroid presented mixed neoplastic cellularity as well as mesenchymal and epithelial cells. Metastases of the mesenchymal component were observed in the kidneys, heart, and musculature, while there was an invasion of neoplastic epithelial cells in the lung. On the IHC, there was positive staining for thyroglobulin, TTF-1, and vimentin. The histopathological and IHC findings indicated a metastatic malignant mixed thyroid neoplasm.