Biological and clinical advances in the understanding of tumor immunology suggest that immune responsiveness of human tumors is a complex biological phenomenon that could be best studied by a real-time comparison of tumor/host interactions in the tumor microenvironment through a high-throughput discovery-driven approach. This conclusion is derived from our recognition that too many hypotheses or, in other words, no solid single hypothesis exist, based on experimental results, to further drive experimentation in human subjects. Functional genomic studies entertained during the last few years consolidated the belief that in humans the interactions between tumor and immune cells are too complex to be approached exclusively with a hypothesis driven method. We believe that immune cells suit cancer cells in a Yin and Yang balance by opposing and yet mutually depending on each other. Indeed, immune infiltration in tumors may play a dual role modulating in different circumstances cancer cell growth or destruction through a physiological modulation of inflammation. It is reasonable to question what induces inflammation at the tumor site. We hypothesize that inflammation is primarily driven by the phenotype of tumor cells that can modulate their microenvironment through cell-to-cell interactions or the secretion of soluble factors. Thus, in analogy the observation of immune cells within tumors parallels the presence of paramedics, police and firemen at the scene of an accident, which is reactive to and not causative of the occurrence. In this review we will explore this hypothesis by reporting and summarizing most of our recent work in the frame of available literature on the subject.
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