Lots of news lately, regarding how anal sex increases the risk for anal cancer...
http://www.fascrs.org/patients/conditions/anal_cancer/
Search/Google "anal sex anal cancer" for more.
Not sure if there is any truth to it all, but I'm certain we'll be hearing more about this theory in the future.
Some even blame anal sex for Farrah Fawcett's death...
Search/Google "Farrah Fawcett anal sex" for more.