Follicular Dendritic Cell Sarcoma of the Thyroid Gland in a Patient with Preexisting Hashimoto's Thyroiditis: A Rare Case Report with a Literature Review.

Thyroid follicular dendritic cell sarcoma (FDCS) is an extremely rare malignancy that originates from follicular dendritic cells of the thyroid germinal centers. To the best of our knowledge, there are only 4 reported cases of thyroid FDCS in the English literature. Herein, we present the fifth case of FDCS of the thyroid gland. A 63-year-old woman presented with a painless midline neck mass, enlarging for the last 4 months. Physical examination revealed a 6-cm nonmobile, firm, multinodular thyroid mass with palpable cervical lymphadenopathy. Due to high suspicion for thyroid malignancy, the patient underwent total thyroidectomy with bilateral modified radical neck dissection. Histologic evaluations revealed sheets of storiform eosinophilic tumoral cells with prominent nucleoli containing multinucleated giant cells, and subsequent immunohistochemistry showed immunoreactivity for CD4, CD21, CD35, CD45 (LCA), and CD68. The patient was started on 6 cycles of doxorubicin, ifosfamide, and radiotherapy. She has had monthly thyroid ultrasonography and contrast-enhanced thoracoabdominal CT scan every 3 months for detecting potential recurrence and/or metastasis screening. Fortunately, 8 months after the operation, the patient is alive without any signs of local or distant metastasis.