Lymphoproliferative process with natural killer cell phenotype. Histopathologic, ultrastructural, and surface marker...

We describe the clinical, structural, and immunophenotypic characteristics of a lymphoproliferative process characterized by persistent thrombocytopenia and prominent involvement of the spleen and, to a lesser degree, the liver. The proliferating cells lacked cytoplasmic azurophilic granules by light microscopy and on ultrastructural examination displayed prominent interdigitating cell processes and did not contain parallel tubular arrays. Immunophenotypically, the cells displayed markers of true natural killer cells (positive CD2, CD56, CD45, CD7, CD16, and CD33). No involvement of peripheral blood or bone marrow was detected. This case represents a proliferation of true natural killer cells probably arising in the spleen. The relationship of this process to other lymphoid proliferations at different sites with true natural killer cell or natural killer-like activity is unknown.