Abstract

Follicular dendritic cells are antigen-presenting immune accessory cells of mesenchymal origin. Follicular dendritic cell sarcomas (FDCS) typically occur in nodal and extranodal sites. However, presentation in the extremity has rarely been reported. A woman in her 60s had a painless, slow-growing right posterior thigh swelling, which had been present for 9 months. Imaging revealed a subcutaneous lesion in the posterior aspect of the right mid-thigh. Fine-needle aspiration cytology from the lesion was suggestive of a malignant spindle cell neoplasm, and she underwent its wide local excision. Immunohistochemistry showed expression of epithelial membrane antigen and CD35, but an absence of cytokeratin, desmin, CD23 and S100. The Ki-67 index was low and a diagnosis of FDCS was made. The lack of clinical guidelines was a challenge in the treatment of this rare case. A multidisciplinary board discussion played a critical role in the planning of the patient’s adjuvant treatment.