Lance Armstrong on Saturday shrugged off the US Anti-Doping Agency's decision to file formal doping charges against him, saying he wouldn't let it halt his cancer awareness work.

"I refuse to be distracted by @usantidoping's antics," the seven-time Tour de France champion wrote on Twitter, a day after the USADA announced it had filed the charges that could cost him his seven titles in the world's most prestigious cycling race.

"It's 2012, I'm gonna continue to lead @LIVESTRONG, raise my 5 kids, and stay fit!" Armstrong tweeted.