More than 100 diseases in which cells grow out of control and can destroy healthy tissue. Caused by failures in the mechanisms that control growth, proliferation and apoptosis. Results from genetic damage (mutation) or altered gene expression. Changes found in cancer cells: uncontrolled growth! many check points that regulate normal cell proliferation such as: autocrine stimulation, contact inhibition, cell death and gap junctions. these check points are somehow skipped = uncontrolled cell growth, autocrine stimulation: cancer cells secrete signalling molecules that act on the same cell they were secreted from. They allow for increased growth and proliferation: contact inhibition: normal cells slow their proliferation rate as they begin to contact other cells. This is inhibited in cancer cells: cell death: cells do not undergo programmed cell death (apoptosis) and are not killed by irradiation. Irradiation normally causes cells to undergo apoptosis to prevent a mutated cell from continuing to replicate: gap junctions: cancer cells do not have gap junctions.