Stimulation of megakaryocytopoiesis and platelet production during growth of an experimental lymphoma

The effect of malignant tumor growth on host's megakaryocytopoiesis and pla telet production was studied in mice bearing transplantable Dalton's lympho ma. Tumor growth was paralleled by thrombocytosis, neutrophilia, and anemia . Platelet Cr-51 half-life was normal but incorporation of 75 Selenomethion ine into circulating platelets was significantly enhanced in the tumor bear ers suggesting stimulated thrombopoiesis while platelet life span remained unchanged. Megakaryocytes and their precursors, the small acetyl cholineste rase positive cells, were found in increased numbers in the bone marrow (BM ) and particularly in the spleen where five to eight-fold rise was observed at the log phase of tumor growth. In addition, a remarkable increase in th e number of megakaryocyte progenitors (CFU-MK and MK CFU-S) was observed bo th in the BM and spleen. Stimulation of these progenitors was more pronounc ed in the spleen than in the marrow, and the change was noticeable even fro m the third day of tumor bearing. Therefore, the results suggest that throm bocytosis associated with the growth of this experimental lymphoma was due to accelerated platelet production following stimulated megakaryocytopoiesi s especially in the spleen.