Viruses' that are genetically modified can be used to treat cancer. This modification removes two key genes in the viruses' genome. The first gene removed is a key gene that is necessary for implementing viral properties in normal cells but not in cancer cells. Therefore, by removing that particular gene the opposing effects occur. The virus cannot infect normal cells but can infect cancer cells. The second gene removed is a gene that the virus normally uses to evade immune system surveillance, by removing this gene the virus can be attacked by the immune system and thus attacking the cancer cells. Researchers hope that genetically modified viruses can be used in the future as a critical treatment option as well as in combination with other therapeutic strategies.