(Reuters) - Lance Armstrong has stepped down as chairman of the cancer charity he founded, Livestrong, after U.S. anti-doping officials issued a scathing report detailing his use of performance-enhancing drugs for years as one of the world's premier cyclists, the foundation said on Wednesday.

Separately, one of his main corporate sponsors, Nike Inc., said it was ending its sponsorship of Armstrong.

"To spare the foundation any negative effects as a result of controversy surrounding my cycling career, I will conclude my chairmanship," Armstrong said in a statement.

Armstrong is set to lose his record seven Tour de France titles after the U.S. Anti-Doping Agency published a 1,000-page report last week that said the now-retired American took part in and organized an elaborate and sophisticated doping scheme on his way to his unrivalled success on the Tour.

Armstrong has always denied he took banned substances during his glittering career but refused to challenge the USADA charges against him.

Armstrong founded the Lance Armstrong Foundation in 1997 after being diagnosed with testicular cancer in late 1996. The foundation launched Livestrong in 2003 to provide support services to cancer patients.

Meanwhile, Nike, in reversing its earlier stand in support of Armstrong, said it could no longer ignore the evidence of his illicit behavior as a professional cyclist.

"Due to the seemingly insurmountable evidence that Lance Armstrong participated in doping and misled Nike for more than a decade, it is with great sadness that we have terminated our contract with him," the company said in a statement. "Nike does not condone the use of illegal performance enhancing drugs in any manner."