Clusterin expression distinguishes follicular dendritic cell tumors from other dendritic cell neoplasms: report of a novel follicular dendritic cell marker and clinicopathologic data on 12 additional follicular dendritic cell tumors and 6 additional interdigitating dendritic cell tumors.

While tumors of dendritic cell lineage may have overlapping histomorphologic features, most but not all cases can be classified using an immunohistochemical panel, including CD21, CD23, CD35, CD1a, and S-100. Based on observations that clusterin is expressed in benign follicular dendritic cells, clusterin expression in 32 dendritic cell tumors was evaluated. Diffuse strong staining for clusterin was seen in 12 of 12 follicular dendritic cell tumors. Two of these cases were negative for traditional markers (CD21, CD23, CD35); they were classified based on characteristic ultrastructural features. Three of 6 interdigitating dendritic cell tumors were negative for clusterin and 3 showed focal weak positivity. Clusterin staining in Langerhans cell histiocytosis ranged from negative (6 of 14) to weak/moderate (8 of 14). Follicular dendritic cell tumors behaved as benign tumors or low-grade sarcomas. Interdigitating dendritic cell tumors demonstrated a widely variable behavior, ranging from benign to rapidly fatal disease. Based on this initial study, strong clusterin staining supports a diagnosis of follicular dendritic cell tumor. Thus, staining for clusterin is useful in classification of dendritic cell tumors, particularly when the more common markers of follicular dendritic cells are not expressed.