Follicular Dendritic Cell Sarcoma : Differential
The differential diagnosis of follicular dendritic cell sarcoma (FDCS) depends upon the location of the tumor and includes many entities. FDCS has to be differentiated from interdigitating dendritic cell sarcoma, dendritic cell sarcoma (NOS), thymoma, spindle cell carcinoma, malignant melanoma, gastrointestinal stromal tumor, undifferentiated pleomorphic sarcoma, and low-grade sarcomas. Some cases (in liver and spleen) resemble inflammatory pseudotumor. Sheets of spindle cells in whorled configuration may resemble meningioma.
CD21 and CD35 are highly specific for FDCS and their presence is required for the diagnosis. FDCS is negative for keratins, where as thymoma and spindle cell carcinoma are strongly positive. The presence of HMB-45, S-100, melan A would support the diagnosis of malignant melanoma.
The image shows a proliferation of uniform spindled cells in whorled, fascicular, and storiform configurations, admixed with small lymphocytes.