STIMULATION OF THROMBOPOIESIS IN MICE BEARING EXPERIMENTAL-TUMORS

Significant increase (p < 0.05) in circulating platelet counts was observed in a wide spectrum of experimental tumors in mice. The mechanism of this abnormality was investigated in strain A mice bearing a transplantable ascites tumor, Sarcoma 180 (S 180). Thrombocytosis observed in the tumor hosts was not due to prolonged platelet survival, as Cr-51 platelet half-life was normal. On the other hand, stimulation of thrombopoiesis, expressed in terms of platelet Selenomethionine-75 (SeM)-Se-75 incorporation, appeared to be the primary reason for elevated platelet counts in the tumor-bearers. Evaluation of thrombopoietic activity in the femoral marrow and spleen by measuring organ uptake of (SeM)-Se-75 and megakaryocyte counts indicated that tumor-induced stimulation in thrombopoiesis may be attributed to enhancement in splenic activity. Pretreatment of normal mice with tumor ascites or tumor cell-conditioned medium resulted in enhancement in thrombopoiesis. The findings suggest the production of some factor(s) by the tumor cells which probably mediate the stimulation of platelet production in tumor hosts.