Tumour immunology refers to the interaction of immune cells with cancer cells. T cells and natural killer cells are involved in tumour immunosurveillance. Tumour immunology is a collaborative branch of biology that is concerned with the role of the immune system in the advancement and evolution of cancer; the familiar application is cancer immunotherapy, which utilises the immune system as a treatment for cancer. Within the tumour microenvironment, a broad spectrum of host responses may be generated, which may range from protective cytotoxic reactions to tumour-promoting inflammatory reactions. The specific factors that dictate the outcome of the anti-cancer response remain under active study, but tumour cells typically exploit host factors to foster disease progression and create a local immunosuppressive network.