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Viral pathogens can cause a cell to become cancerous through the mechanisms which enable their survival. One basic mechanism in the viral life cycle is the "hijacking" of host cell transcription machinery. Viruses can manipulate the host cell into creating viral proteins while inhibiting production of host cell proteins, they may also integrate viral DNA into host DNA producing abnormal proteins or a disruption in the quantity of certain proteins. This change in DNA can also cause mutation in genes creating cancerous cells no longer able to function properly. Another reason viruses may promote cancer is through the different mechanisms they use to evade the immune system.A virus can inhibit anti-viral pathways set up by the innate immune system, they also create an environment which suppresses the cells ability to not only recognize a cancerous cell but the appropriate responses required to shut down that cell. There are different examples of viruses promoting cancer, some interfere with cell signaling, tumor suppression, or targeting immune cells directly. Often cancer cells appear and thrive because of the indirect effect viruses have on both cells and the general area of infection. Inflammation is a complex mechanism the innate immune system uses to target and block an infected area but can also cause damage to healthy host cells and result in cancerous activity.
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