Case of Malignancy Arising from Giant Cell Tumour of Soft-tissue Involving Thyroid Mimicking Thyroid Carcinoma: A Potential Pitfall.

Giant Cell Tumour of soft-tissue (GCT-ST) is a rare neoplasm which is morphologically similar and genetically unrelated to GCT bone and included under intermediate rarely metastasising category. They are reported predominantly in superficial soft-tissue of the upper and lower extremities and less frequently in head and neck. The authors present a case of malignancy arising from GCT-ST involving thyroid gland mimicking primary thyroid malignancy. An 80-year-old female presented in the Outpatient Department (OPD) with a neck swelling of six months duration and sudden increase in size and hoarseness of voice for two weeks. An upfront surgery was planned with a clinical suspicion of primary thyroid neoplasm. Intraoperatively, the thyroid gland was replaced by multiple nodules, which were seen infiltrating adjacent structures. Due to the invasive nature, only a subtotal thyroid resection was done. The histopathology showed predominantly neoplasm composed of mononuclear cells and sheets of osteoclast like giant cells with foci showing features of malignancy. Histomorphology along with Immunohistochemistry (IHC) confirmed a diagnosis of GCT-ST involving the thyroid gland. Due to the rapidly progressive nature of the disease, the patient succumbed within two months. [ABSTRACT FROM AUTHOR]