Reticulum cell sarcoma of lymph node with mixed dendritic and fibroblasticfeatures

We report a case of clinically aggressive reticulum cell sarcoma with mixed follicular dendritic cell (FDC) and fibroblastic reticular cell (FRC) feat ures. Histologically, the tumor was confined to lymph nodes occurring as a multifocal epitheliold and spindle cell proliferation with appreciable mito tic rate and numerous admixed non-neoplastic B-cells. Ultrastructural exami nation revealed elongated cells with prominent nucleoli, interdigitating ce ll processes and frequent desmosomes. These features are typical of FDC sar coma. However, immunohistochemical stains showed no expression of antigens characteristic of FDCs, including CD21, CD23 and CD35. Cytogenetic characte rization of this tumor, by conventional G-banding and multicolor spectral k aryotyping, revealed multiple clonal chromosomal aberrations, including del (X)(p11.4) and add (21) (p11.2). Gene expression analysis by cDNA microarra y of RNA obtained from short-term tumor cultures revealed high-level expres sion of a set of genes (including PDGF receptor-alpha and -beta, certain me talloproteinases, and CD105) that were also highly expressed in cultures of nodal FRC cultured from non-neoplastic lymph nodes. We propose that this t umor represents a nodal sarcoma with intermediate differentiation between F DCs and FRCs. This case adds to the diversity of tumors that may arise from lymph node stroma and supports a possible relationship between the FDC and FRC lineages.