Two siblings exhibiting a histiocytic proliferation in the liver, lymph nodes, skin and bone marrow were presented. The cytological features of the proliferating cells were benign-appeared, characterized by uniform contour, abundant eosinophilic cytoplasm and a relatively small round nucleus with a single nucleoli and finely dispersed chromatin. They showed scanty mitotic figures. Active viral infection was not documented by serological tests or viral culture of the lymph node at the time of diagnosis. We considered that the histiocytic proliferation of the present cases was neoplastic rather than reactive, because the clinical course was rapidly progressive and severe and the patients did not respond to the supporting therapy. Furthermore. the treatment of the older brother with aggressive antineoplastic chemotherapies (VEPA, IM) was successful in inducing and maintaining remission for over thirty months. Although the younger brother responded to the same chemotherapies, no complete remission was obtained.
Since it is very difficult to distinguish morphologically between reactive and malignant nature of the disease, we believe that it might be necessary to manage these patients based on clinical behavior rather than morphology of the histiocytes in the tissues.
