A case of primary histiocytic sarcoma arising from thyroid gland.

Histiocytic sarcoma (HS) is an extremely rare true histiocytic malignancy. We report a case of HS arising from thyroid gland in a 69 year-old man. Following subtotal thyroidectomy, a histopathologic, immunohistologic, and genotypic examination revealed HS. This tumor was composed of large spindle or round epithelioid cells with abundant eosinophilic cytoplasm. The neoplastic cells were positive for macrophage-associated antigen CD68, CD163, and lysozymes, as well as CD45, HLA- DR, DP, DQ, and S100, most consistent with a diagnosis of HS. The BIOMED-2 multiplex PCR analysis showed polyclonal B- and T-cell populations. To our knowledge, this is the first report of a rare entity HS involving thyroid gland using a comprehensive immunophenotyping panel including CD163 as well as molecular studies to establish the true histiocytic nature of these lesions.