Composite dendritic cell neoplasm (NOS) and small lymphocytic lymphoma

This report describes a composite (or "collision") of a dendritic cell neop lasm and small lymphocytic lymphoma. It represents the seventh example of d endritic cell neoplasia occurring in the setting of low-grade B-cell malign ancy and the third example of a composite tumor, in which both neoplasms we re present within the same lymph node. The small lymphocytic lymphoma compo nent exhibited a typical CD20+, CD5+, and CD23+ immunophenotype. The dendri tic cell neoplasm exhibited reactivity with CNA-42, but nonreactivity for C D21, CD35, smooth muscle actin, desmin, and epithelial membrane antigen (EM A). Equivocal cytoplasmic staining was seen for S100p, CD68, and Factor XII Ia. UItrastructurally, the dendritic cell neoplasm exhibited desmosomes, ro ugh endoplasmic reticulum, cytoplasmic intermediate filaments, and intercel lular collagen. Because the immunophenotype and ultrastructure did not corr espond to one of the five recognizable dendritic cell subtypes, the neoplas m was designated dendritic cell neoplasm, not otherwise specified (NOS). Po lymerase chain reaction (PCR) analysis for immunoglobulin heavy chain gene rearrangements performed on individual components of the composite tumor de monstrated rearrangement within the small lymphocytic lymphoma component, b ut none in the dendritic cell component. The lack of an immunoglobulin heav y chain gene rearrangement within the dendritic cell component argues again st a transformational event and supports the concept that these separate ne oplasms represent a true "collision" or composite lesion.