CALCA and undifferentiated carcinoma: With the help of immunohistochemistry and electronic microscopy, it has been shown that most of the sarcomatous lesions of the thyroid gland are undifferentiated carcinomas with sarcomatous differentiation, with epithelial origin and not mesenchymal, which may show expression of vimentin and cytokeratin, besides the occasional expression of thyroglobulin, but do not show the expression of desmin, muscle-specific actin, chromogranin or calcitonin.13