The growth of cancer demonstrates failure of the body's mechanisms to control interactions of some of its cells. This could occur because the cancer cell does not respond to the control signals- whether due to damage to DNA, to presence of the products of the oncogenes, or to altered homeostatic control mechanisms. A variety of different factors that can damage or change DNA in cells cause cancer, including viruses, many different chemicals and ultraviolet radiation. Most normal cells have differentiated, developing specific morphology and function.
Normal cells tend to lose their ability to proliferate during the process of differentiation.
In many tissues, the loss of mature cells is replaced by proliferation of less mature precursor cells followed by differentiation of their progeny. Most cancers probably originate from these precursor cells. First, lymphocytes must enter the tumor site. Th1 lymphocytes should be activated and release appropriate cytokines including interleukin-2, interferon gamma, and tumor necrosis factor beta. B lymphocytes may also be activated to secrete neutralizing antibodies that aid in cancer cell phagocytosis by antigen presenting cells, although their role in tumor immunity is less important.