Lance Armstrong said on Thursday he would not fight doping accusations by the US Anti-Doping agency, a move that appears to put his seven Tour de France titles at risk."I know who won those seven Tours, my teammates know who won those seven tours, and everyone I competed against knows who won those seven tours," Armstrong said in the statement, which was posted on his website.Armstrong also alerted the USADA in a letter sent just before a midnight Thursday deadline that he would not fight the charges through arbitration, according to the newspaper.