British Prime Minister Davis Cameron, centre, is joined by US Secretary of State John Kerry, left, and Nigerian President Muhammadu Buhari, as he speaks at the international anti-corruption summit on Thursday May 12, 2016 in London. British Prime Minister David Cameron on Thursday called corruption a "cancer" at the heart of the world's problems, while U.S. Secretary of State John Kerry said the corruption "pandemic" was as great a threat as extremism. (Dan Kitwood/Pool via AP)