Primary osteosarcoma of the thyroid gland

Abstract

Objective: Primary mesenchymal tumours of the thyroid gland are extremely rare. One percent of the thyroid tumours are reported to be sarcomas, and the infrequency of these lesions is a reason for the difficulties in achieving right diagnosis. Method: We report a case of primary thyroid osteosarcoma (PTO) in 54-years old female who underwent surgery of the thyroid left lobe, with an unexpected final diagnosis, focusing on the histopathological and immunohistochemical features, which helped in differential diagnosis. Results: The surgical specimen was a thyroid lobe measuring 10 × 9 × 8,5 cm. The cut surface showed gritty, grayish-white tumour with areas of hemorrhage which almost entirely infiltrate the left lobe, measuring 9 cm. The microscopic examination showed a high-grade malignant neoplasm with necrotic areas composed of polygonal and fusiform cells, numerous osteoclast-like giant cells and focal osteoid deposition. Immunohistochemical staining showed positive expression for vimentin and osteopontin, and negative immunostaing for cytokeratin 19, epithelial membrane antigen, thyroid transcription factor-1, calcitonin and thyroglobulin, with a high mitotic index (60 %) of the tumour cell nuclei, determinate by Ki-67 antibody. Thus, the diagnosis of PTO of a predominantly teleangiectatic variant was established, that was confirmed with additional CD34 immunohistochemistry. Conclusion: PTO is extremely rare tumour that should be considered in thyroid pathology and immunohistochemistry is of decisive significance.