An<unk>  is a virus that preferentially infects and kills cancer cells. As the infected cancer cells are destroyed by oncolysis, they release new infectious virus particles or virions to help destroy the remaining tumour.<unk> es are thought not only to cause direct destruction of the tumour cells, but also to stimulate host anti-tumour immune system responses.<unk> es also have the ability to affect the tumor micro-environment in multiples ways. The potential of viruses as anti-cancer agents was first realised in the early twentieth century, although coordinated research efforts did not begin until the 1960s. A number of viruses including adenovirus, reovirus, measles, herpes simplex, Newcastle disease virus, and vaccinia have been clinically tested as<unk>  agents. Most current<unk> es are engineered for tumour selectivity, although there are naturally occurring examples such as reovirus and the senecavirus, resulting in clinical trials. The first<unk>  to be approved by a national regulatory agency was genetically unmodified ECHO-7 strain enterovirus RIGVIR, which was approved in Latvia in 2004 for the treatment of skin melanoma; the approval was withdrawn in 2019. An<unk>  adenovirus, a genetically modified adenovirus named H101, was approved in China in 2005 for the treatment of head and neck cancer. In 2015, talimogene laherparepvec (OncoVex, T-VEC), an<unk>  herpes virus which is a modified herpes simplex virus, became the first<unk>  to be approved for use in the U.S. and European Union, for the treatment of advanced inoperable melanoma.
Oncolytic virus
Lentivirus
Helper dependent virus
Oncovirus
Virus
Passenger virus
Oncophage
Flavivirus