The concept of leukocyte-tumor cell fusion as a significant driver of cancer progression has been around a long time, and has garnered growing support over the last several years. The underlying idea seems quite simple and attractive: Fusion of tumor cells (with their inherent genetic instability) with leukocytes, particularly macrophages, could produce hybrids with high invasive capabilities, greatly facilitating their metastatic dissemination, while potentially accelerating tumor cell heterogeneity. While there are a number of attractive features with this story on the surface, the various studies seem to leave us with a conundrum, namely, what is the fate of such fusions?
Keywords: CTCs; MICs; MTFs; macrophage-tumor cell fusions; metastasis; metastasis-initiating cells.