A cytochemical and immunohistochemical approach to malignant histiocytosis.

Malignant histiocytosis (MH) is a true histiocytic disorder, whose identification is still based on too broad morphologic criteria. Using routine histology, cytochemical and immunohistochemical techniques on involved lymph nodes, 15 cases of MH have been investigated. Pleomorphism and cellular atypia, phagocytosis, lack of cohesiveness between proliferating cells, sinusoidal involvement, and plasmacytic infiltrate were the most common histologic features. MGG-stained imprints from 14 cases showed a composite tumor population mainly consisting of histiocyte-appearing cells, poorly differentiated atypical cells, and multinucleated giant cells. These cells, irrespective of cytologic features, revealed a diffuse, moderately to strongly positive reaction with acid phosphatase and nonspecific esterase. Naphthol-AS-D-chloroacetate esterase, Sudan black B, alkaline phosphatase, and beta-glucuronidase reactions were completely negative. Immunoperoxidase studies in 11 cases demonstrated that tumor cells stained positively for both kappa and lambda chains. These cells were also positive for albumin. Polytypic staining for IgG was observed in two cases, and a weak staining for lysozyme was found in two other nodes. Global results confirm the value of these studies for functional profile determination of MH proliferating cells. A combined approach using a variety of cytochemical and immunohistochemical techniques should be routinely considered in MH as useful additional studies for a more precise diagnostic definition of the disease.