Composite dendritic cell neoplasm (NOS) and small lymphocytic lymphoma

This report describes a composite (or 'collision') of a dendritic cell neoplasm and small lymphocytic lymphoma. It represents the seventh example of dendritic cell neoplasia occurring in the setting of low-grade B-cell malignancy and the third example of a composite tumor, in which both neoplasms were present within the same lymph node. The small lymphocytic lymphoma component exhibited a typical CD20+, CD5+, and CD23+ immunophenotype. The dendritic cell neoplasm exhibited reactivity with CNA-42, but nonreactivity for CD21, CD35, smooth muscle actin, desmin, and epithelial membrane antigen (EMA). Equivocal cytoplasmic staining was seen for S100p, CD68, and Factor XIIIa. Ultrastructurally, the dendritic cell neoplasm exhibited desmosomes, rough endoplasmic reticulum, cytoplasmic intermediate filaments, and intercellular collagen. Because the immunophenotype and ultrastructure did not correspond to one of the five recognizable dendritic cell subtypes, the neoplasm was designated dendritic cell neoplasm, not otherwise specified (NOS). Polymerase chain reaction (PCR) analysis for immunoglobulin heavy chain gene rearrangements performed on individual components of the composite tumor demonstrated rearrangement within the small lymphocytic lymphoma component, but none in the dendritic cell component. The lack of an immunoglobulin heavy chain gene rearrangement within the dendritic cell component argues against a transformational event and supports the concept that these separate neoplasms represent a true 'collision' or composite lesion.