(CNN) -- Former pro cyclist Lance Armstrong announced Wednesday he will step down as chairman of the Livestrong cancer charity he founded, a week after an anti-doping group released what it said was evidence that he used banned substances while competing.
The move comes the same day that Nike announced it was ending its endorsement contract with Armstrong amid "seemingly insurmountable evidence" that he participating in doping.
Armstrong, who will remain on Livestrong's board of directors, said his decision was made to "spare the foundation any negative effects as a result of controversy surrounding my cycling career," according to a statement posted to the group's website.
"My family and I have devoted our lives to the work of the foundation and that will not change. We plan to continue our service to the foundation and the cancer community. We will remain active advocates for cancer survivors and engaged supporters of the fight against cancer," Armstrong said.
Last week, the U.S. Anti-Doping Agency said it had uncovered overwhelming evidence of Armstrong's involvement in a sophisticated doping program while a professional cyclist. Armstrong has consistently denied the claims.
Nike said it would continue to support Livestrong initiatives.
Founding chairman Jeff Garvey will take over for Armstrong, the Texas-based organization said.
The organization, which had strongly defended Armstrong's role as recently as last week, did not ask him to step aside, Livestrong spokeswoman Katherine McLane said.
"This was Lance's idea," she said.
Armstrong founded the charity in 1997 after his own successful treatment for testicular cancer that had spread to his brain and lungs. He came back from the disease seemingly stronger than ever, winning the first of his seven Tour de France titles three years after he was diagnosed with cancer.
His success became an inspiration for cancer patients worldwide, spreading his reach far beyond the insular world of cycling and cementing a place in celebrity culture, dating a rock star and appearing in movies. The bright yellow "LIVESTRONG" wristbands distribute by his charity became a potent symbol for perseverance in the face of adversity.
People should look to that legacy in assessing Armstrong, Livestrong President Doug Ulman said in praising the charity's founder.
"Lance's devotion to serving others whose lives were irrevocably changed by cancer, as his was, is unsurpassable," he said in the statement. "We are incredibly proud of his record as an advocate and philanthropist and are deeply grateful that Lance and his family will continue to be actively involved with the Foundation's advocacy and service work."
In its report, the anti-doping agency made public testimony from Armstrong's teammates and others involved in the U.S. Postal Service- and Discovery-sponsored cycling teams who said the seven-time Tour de France winner was among team members who used banned performance-enhancing substances and tried to hide it from testing officials.
Armstrong has said he never has failed a drug test and has consistently denied participating in any banned practices. Armstrong's lawyer, Tim Herman, called the report last week a "one-sided hatchet job" and a "government-funded witch hunt."
Last week, Ulman also defended Armstrong against the doping charges, issuing a statement saying USADA appeared to be "motivated more by publicity rather than fulfilling its mission." In that October 10 statement, he lauded Armstrong for his achievements "both on and off the bike."
McLane also noted the day of the report's release that donations to the charity had boomed since August, when Armstrong announced he was ending his legal fight to stop USADA's investigation.
According to Livestrong, Armstrong has helped raise nearly $500 million for cancer research, treatment and support in his role as Livestrong founder and helped "dispel the stigma and misconceptions about the disease."
McClane said Wednesday that Livestrong's audience -- cancer patients and their families -- aren't troubled by Armstrong's woes.
"The last thing that's going to enter your mind is news from the cycling world," she said.