Blastic natural killer (NK)-cell lymphoma: report of an unusual CD4 negative case and review of the CD4 negative neoplasms with blastic features in the literature.

Blastic Natural Killer (NK)-cell lymphoma is a relatively new entity which has been recently included in the WHO classification. CD4 expression is observed in most cases of blastic NK-cell lymphomas and has been related with skin tropism. We report an unusual CD4 negative blastic NK-cell lymphoma with primary presentation in the skin, subsequent infiltration of the bone marrow and aggressive behavior.