CD4+/CD56+ hematodermic neoplasm: report of a rare variant with a T-cell receptor gene rearrangement.

CD4+/CD56+ hematodermic neoplasm (HN), formerly known as a blastic natural killer (NK) cell lymphoma, is a rare subtype of a cutaneous dendritic cell neoplasm notable for highly aggressive behavior. The characteristic features are: expression of the T-helper/inducer cell marker CD4 and the NK-cell marker CD56 in the absence of other T cell or NK-cell specific markers. In particular, CD3 (surface or cytoplasmic) and CD2 are not expressed. Although T-cell receptor (TCR) genes are generally reported to be in a germline configuration, we present an unusual variant of a CD4+/CD56+ HN with a clonal rearrangement of TCR genes. This feature of a CD4+/CD56+ HN has been only rarely reported. Recognition of the presence of clonal TCR gene rearrangements in a small subset of CD4+/CD56+ HN is important to avoid misdiagnosis of this entity as an unusual variant of a cutaneous T-cell lymphoma.