The role of the immune system in cancer

Abstract

Abstract Infection and chronic inflammation predisposes us to many forms of cancer and the response to malignant disease shows many parallels with inflammation and wound healing. The cells involved in inflammation are detected in a range of common cancers, together with the inflammatory cytokines and members of the chemokine ligand/receptor systems. Many cancers occur more frequently with certain infectious diseases; examples include Helicobacter pylori infection, human immunodeficiency virus, hepatitis, and human papillomavirus (HPV). The longer the infection and inflammation persist, the higher the risk of associated cancer. Chronic inflammatory conditions such as inflammatory bowel disease, have a five-to sevenfold higher incidence of colon cancer, as a result of the immune response causing colonic epithelium to become transformed. Therefore, understanding these disease processes may lead to better prevention and treatment for cancer. The theory of immune surveillance suggests that the immune system continually recognizes and eliminates tumours; when a tumour escapes immune surveillance and grows too large for the immune system to kill, cancer can result. Immune surveillance is most likely to be successful against virusinduced cancers that express foreign peptides. However, tumours vary greatly in their immunogenicity, and even those with antigens, which can be recognized by the host immune system, can evade immune elimination. Lack of tumour rejection by intact immune systems is not always due to the absence of antigens that can be recognized or to the absence of T cells that can recognize those antigens. Tumour-specific lymphocytes can be found in the blood, draining lymph nodes, and in the tumour itself of patients with actively growing tumours. These lymphocytes can kill tumour cells in vitro but fail to do so in vivo. The presence of these cells has allowed immunologists to identify antigens on some tumour cells.