Follicular dendritic cell sarcoma of the tonsil: A case report of uncommon tumor displaying diagnostic features and review of the literature

Introduction: Follicular dendritic cells are non-hematopoietic cells that are found in germinal centers and function in the differentiation and development of activated B cells. Follicular dendritic cell sarcoma is a rare neoplasm, typically, located in lymph nodes throughout the body. Follicular dendritic cell sarcomas can also be found in extranodal sites. Follicular dendritic cell sarcomas located in extranodal sites are underdiagnosed due to the rarity and lack of consideration in differential diagnoses. Additionally, up to one-third of extranodal cases are misdiagnosed. Case Report: We are presenting a case of follicular dendritic cell sarcoma located in the tonsil of a 73-year-old male. Examination revealed a tonsillar mass suspicious for squamous cell carcinoma, malignant melanoma, or anaplastic lymphoma. Biopsy of the tonsil was performed and the patient was diagnosed with a low-grade malignant tumor exhibiting morphologic and immunohistochemical features indicative of dendritic/reticulum cell origin. Conclusion: The reporting of this case aims to increase knowledge and awareness regarding the morphologic and immunohistochemical features of rare and often misdiagnosed extranodal follicular dendritic cell sarcomas. Heightened awareness of this tumor will lead to inclusion as a differential diagnosis of the initial evaluation of biopsy with this tumor features and avoid misdiagnosis.