Primary pulmonary follicular dendritic cell neoplasm: a case report and review of the literature.

Follicular dendritic cell tumor (FDCT) is an uncommon neoplasm that typically presents as a slow-growing, painless mass without systemic symptoms. Histologically, FDCT is characterized as a proliferation of spindle to ovoid cells having plump eosinophilic cytoplasm with indistinct borders and nuclei with vesicular or granular chromatin and small distinct nucleoli. The immunohistochemical profile of FDCT includes positive staining for CD21, CD23, CD35, vimentin, fascin, HLA-DR, epithelial membrane antigen, clusterin, and D2-40. Follicular dendritic cell tumor occurs primarily in lymphoid tissue; however, involvement of extranodal sites such as the tonsils, spleen, and gastrointestinal tract has been reported. Lung involvement typically represents metastatic disease with, to our knowledge, only 2 prior cases of extranodal primary FDCT of the lung reported. We report the third case of primary pulmonary FDCT arising in a 64-year-old woman.