Cancer is a major public health problem worldwide. Accumulating evidence suggests that Gtumor-host interactions may in part impact on tumor progression. However, the role of inflammation and adaptive immune reaction in cancer emergence, local and metastatic invasion and recurrence are still not dearly defined. Pro-inflammatory mediators are suspected to favor tumor growth and angiogenesis and naturally generated T cells with antigenic specificity to tumor associated antigens were usually in a state of anergy. Nevertheless, experiments in mouse and human showed a significant association between high density of tumor infiltrating T cells and improved cancer prognosis. Recently, the global analysis of colorectal cancer microenvironment demonstrated that a strong and coordinated Th1 adaptive immune response within primary tumors dramatically reduced the risks of relapse events. Interestingly the absence of early signs of metastatic invasion (lymphovascular emboli) correlated with a significant increase of the density of memory T cells in situ. This chapter presents the arguments supporting the existence of immunosurveillance mechanisms in human cancer. We will discuss the potent role of memory T cells in cancer immunity as well as the opportunities of therapeutic strategies uncovered by this new area of investigation.