IL6 and neoplasm: Because the metastasis-promoting effects of MDSCs in this study occurred in the absence of adaptive immunity and natural-killer cell activity and there was no increase in IL-6 signaling in the spleen, MDSCs themselves must have directly increased tumor cell metastatic capability in the tumor sites, either primary tumors or metastases, but not in the lymphoid organs, affecting both the afferent and efferent phases of metastasis through exaggerated IL-6 trans-signaling.