On the terms “reticulosis” and “reticulum cell sarcoma” with regard to the modern concept of the monocyte macrophage system

Summary The terms reticulosis and reticulum cell sarcoma (= malignant lymphoma, histiocytic type) are discussed regarding the modern concept of the monocyte macrophage system which today has replaced the ancient theory of the reticuloendothelial system. The monocyte macrophage system is not independent, but closely related to the myeloid system. Thus, a third blood forming system as was believed in the case of RES does not exist. Phagocytic reticulum cells of the various hematopoietic organs are highly activated monocyte-derived macrophages. All those conditions formerly termed reticuloses have been found to belong either to the myeloid or to the lymphatic system. Considering the reticulum cell sarcomas or malignant histiocytic lymphomas, most of them seem to be of lymphatic rather than of macrophage origin, representing highgrade malignant lymphomas, possibly immunoblastic sarcomas. No relationship between these tumours and the monocyte macrophage system has been established, so far. Therefore, the terms reticulosis and reticulum cell sarcoma should be no longer used in order to avoid confusion, in order to stimulate sufficient diagnostic efforts which will really clarify such cases, and in order to give full credit to modern results of hematopathology.