Tumour-cell migration, invasion, and metastasis: navigation by neurotransmitters

Cancer starts as a localised disease, which, if detected early, can often be treated successfully by removal of the primary tumour. A pernicious progression is the invasion of tumour cells into surrounding tissues, resulting in development of distant metastases. Because active migration of tumour cells is a prerequisite for tumour-cell invasion and metastasis, a pressing goal in tumour biology has been the elucidation of factors regulating the migratory activity of these cells. The most prominent regulatory factors are ligands to serpentine receptors-eg, chemokines and neurotransmitters. Many types of neurotransmitter receptors are expressed on tumour cells, supporting the theory that psychosocial factors are involved in the progression of cancer. Understanding how such receptors regulate migration and the availability of specific receptor antagonists could open up new avenues for chemoprevention of tumour-cell migration and metastatic development.