Simian Virus 40 (SV40) is a polyomavirus originally discovered in the early 1960s in monkeys. It is known for its ability to infect cells and potentially cause tumors in laboratory animals. SV40 is often studied in the context of cancer research due to its interactions with cellular mechanisms. In humans, SV40 was found as a contaminant in some polio vaccines administered in the 1950s and 1960s. While it raised concerns about its potential link to cancer, extensive research has not conclusively established a direct connection between SV40 and human cancers.