The potential for a link between viruses and cancer has been around for over a century, but only in this century has the study taken off. The link may involve cell fusion, causing chromosome instability.
Perhaps even more exciting is where this research is leading to, namely a new understanding of how genes work, for both good and ill.
Viruses have simple genetic codes, known to pick the locks of cells and cause disease. All of us are based on more complex DNA structures, and their contents -- the human genome -- is just one manifestation of them.
To say that a line of genetic material contains so much adenine and so much guanine, arranged in this specific order, turns out to be only the first step in understanding how DNA works. Viruses are trying to teach us something, and where we are when we learn that language may be a different scientific country.
It reminds me a bit of the end of Stephen Spielberg's "Close Encounters of the Third Kind," in which the aliens transmit what seems at first to be a simple collection of sounds that turn out to be an entry into something much more important. (You can add the film to your collection at Amazon.Com.)
Call this close encounters of the cellular kind.