Sarcoma arising in hyaline-vascular castleman disease of skin and subcutis

We report on a case of a sarcoma arising in the hyaline-vascular variant of Castleman disease (HVCD) of the skin and subcutis. The patient was a 38-year-old man who clinically presented with a subcutaneous non-fixed cyst-like mass on his right shoulder with an unremarkable prior medical history. Histologic sections showed a biphasic tumor with numerous atretic lymphoid follicles located in the deep dermis and subcutis and a spindle-cell neoplasm mainly situated in the deep subcutis and adjacent soft tissue. The atretic lymphoid component fulfilled the criteria for HVCD, whereas the spindle-cell lesion showed all the criteria for sarcoma including nuclear atypia and frequent mitotic figures. The sarcomatous component was diffusely positive for fascin, nerve growth factor receptor, and CD34 with focal weak reactivity for CD21 and CNA.42. Stains for CD23, CD31, CD35, CD99, ALK-1, SMA, ASMA, desmin, factor XIIIa, AE1-AE3, EMA, bcl-2, S-100, Melan-A, HMB-45, Cam 5.2, and factor VIII were negative in the neoplastic spindle cells. No monoclonal population of lymphocytes was detected and we could not identify EBV or HHV-8 virus by PCR. Electron microscopy of the sarcomatous component showed spindle cells with labyrinth-like invaginations of the nucleus and numerous long, slender, interwoven cytoplasmic processes. The sarcomatous component in this case is most consistent with a poorly differentiated follicular dendritic cell sarcoma based upon the morphologic and ultrastructural findings.