Malignant histiocytosis: A phenotypic and genotypic investigation

Ten cases of malignant histiocytosis (MH) were evaluated for clinical and histopathologic features, phenotype, and rearrangement of T cell receptor (TCR) β, γ, and α and immunoglobulin (Ig) genes (7/10). All cases were HLA-DR+ and CD30-positive. Four cases had molecular evidence of T cell lineage such as TCR β, γ, and α rearrangements, and one additional case synthesized the cytoplasmic TCR β chain. The remaining five cases did not show unequivocal T, B, natural killer (NK) cell, or macrophagic origin, and three of them had germline TCR and Ig genes. Ultrastructural analysis was not helpful for the definition of the cell lineage. Most myelomonocytic markers (MAC387, CD13, CD14, CD64, CD68) were either negative on the MH cells or were expressed on cells with rearranged TCR gene. Precursor (CD34, CD7) and NK (CD16, CD56, and CD57) cell markers were not found. The lineage of a number of cases of MH remains unresolved.