Never one to back away from a fight, Lance Armstrong is finally giving in and the cost of quitting is steep: His seven Tour de France titles could be gone as soon as Friday.

The superstar cyclist, whose stirring victories after his comeback from cancer helped him transcend sports, chose not pursue arbitration in the drug case brought against him by the U.S. Anti-Doping Agency. That was his last option in his bitter fight with USADA and his decision set the stage for the titles to be stripped and his name to be all but wiped from the record books of the sport he once ruled.

Travis Tygart, USADA's chief executive, left no doubt that was the next step. He said Armstrong would lose the titles as soon as Friday and be hit with a lifetime ban, even though he is retired and turning 41 next month.

Still to be heard from was the sport's governing body, the International Cycling Union, which had backed Armstrong's legal challenge to USADA's authority. Tygart said the UCI was "bound to recognize our decision and impose it" as a signer of the World Anti-Doping Code.

"They have no choice but to strip the titles under the code," he said.

Armstrong clearly knew his legacy would be blemished by his decision. He said he has grown tired of defending himself in a seemingly never-ending fight against charges that he doped while piling up more Tour victories than anyone ever. He has consistently pointed to the hundreds of drug tests that he passed as proof of his innocence during his extraordinary run of Tour titles from 1999 to 2005.

"There comes a point in every man's life when he has to say, `Enough is enough.' For me, that time is now," Armstrong said Thursday night, hours before the deadline to enter arbitration. He called the USADA investigation an "unconstitutional witch hunt."

"I have been dealing with claims that I cheated and had an unfair advantage in winning my seven Tours since 1999," he said. "The toll this has taken on my family and my work for our foundation and on me leads me to where I am today - finished with this nonsense."

USADA treated Armstrong's decision as an admission of guilt, hanging the label of drug cheat on an athlete who was a hero to thousands for overcoming life-threatening testicular cancer and for his foundation's support for cancer research. Armstrong could lose other awards, event titles and cash earnings, and the International Olympic Committee might look at the bronze medal he won in the 2000 Games.

"It is a sad day for all of us who love sport and athletes," Tygart said. "It's a heartbreaking example of win-at-all-costs overtaking the fair and safe option. There's no success in cheating to win."

While Tygart said the agency can strip the Tour titles, Armstrong disputed that, insisting his decision is not an admission of guilt but a refusal to enter an arbitration process he believes is unfair.

"USADA cannot assert control of a professional international sport and attempt to strip my seven Tour de France titles," he said. "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."