Cytomegalovirus and Cancer: A Long and Winding Road to Conclusive Evidence

It has long been known that collecting convincing evidence relating a certain virus to the formation of one or more cancer type(s) is a tedious task. In 1911, Peyton Rous, being aware of similar previous experiments on the transmission of leukaemias between chicken by Vilhelm Ellerman and Olaf Bang [1], had shown that cell-free extracts from chicken sarcomas induced sarcomas in healthy chickens [2]. He concluded that a “minute parasitic organism” or a “chemical stimulant, elaborated by the neoplastic cells” must be responsible for sarcoma formation [2]. Later, the causative agent was identified to be a retrovirus and called the Rous sarcoma virus (RSV) [3]. However, it took 55 years and the discovery of the Epstein-Barr virus, the first human tumour virus [3,4], before Peyton Rouse eventually received the Nobel Prize for his work in 1966.