The microbiome - the distinct populations of microbes that inhabit various surfaces and microenvironments in and on the human body- has increasingly been implicated as a determinant of human health. In the context of cancer, the composition and characteristics of the microbiome are being shown to directly impact the pathogenesis of cancer, anti-tumor immunity and therapeutic response. The objectives of this symposium is to explore the host-tumor-microbiota interactions and underlying mechanisms that drive these processes, and how the microbiome can be manipulated to improve patient health and survival.