Abstract
INTRODUCTION: Follicular dendritic cell sarcoma (FDCS) is a rare neoplasm of antigen-presenting cells within the reticuloendothelial system primarily originating in lymph nodes, but in almost one-third of the patients, extranodal sites are involved including oral cavity, tonsil, gastrointestinal tract, soft tissue, and breast. The thyroid gland is an extremely rare location for FDCS and very few cases are reported in the literature. CASE REPORT: Here, we present a 39-year-old man who presented with a swelling in the neck for 3 months and difficulty in breathing for 15 days. Following left hemi-thyroidectomy, histopathologically and immunohistologically, he was diagnosed as FDCS of thyroid arising in Castleman's disease. He received adjuvant radiation treatment. The patient had favorable prognosis with no evidence of disease for 6 years after treatment till date. CONCLUSION: The aim of this report was to present the rare site of FDCS arising in the thyroid gland, the vital role of immunohistochemistry in diagnosis, and effectiveness of multimodality treatment for favorable prognosis.