(NEW YORK) -- Before his disgrace, Lance Armstrong was known for his seven Tour de France victories, his comeback from cancer and the yellow bracelets of his foundation, Livestrong.
Armstrong launched the cancer charity after being diagnosed with a testicular tumor in 1996. The cancer had spread to his abdomen, lungs and brain, but he beat the odds to survive and continue his spectacular -- or notorious -- racing career.
Now that Armstrong's titles have been tainted by his admitted use of performance-enhancing drugs, questions have also been raised about whether those banned substances caused or contributed to his cancer.
The answer is not as clear cut as a confession for cheating.
"One could infer that these agents could potentiate the growth of a cancer cell," said oncologist Dr. Arjun Vasant Balar of NYU Langone Medical Center in New York, describing how steroids, growth hormones and erythropoietin fuel cell division and growth. "Could they create a cancer cell? That's unclear. We don't know."
While studies in cells and lab animals have linked doping agents to cancer, evidence in humans is anecdotal at best.
"Several cases of cancers associated to the use of anabolic steroids as doping practice have been reported," said Dr. Lucio Tentori, a cancer researcher at the University of Rome Tor Vergata and author of a 2007 review on doping and cancer risk. "Unfortunately, to evaluate this cancer risk in controlled clinical studies is difficult since these substances are frequently used at very high doses and in combination with other licit or illicit drugs."
Despite the dearth of human research, Tentori wrote in his report that "athletes should be made aware that long-term treatment with doping agents might increase the risk of developing cancer."
Armstrong might have suspected as much, according to Betsy Andreu, the wife of Armstrong's former friend and teammate Frankie Andreu. Andreu testified in an insurance-related civil suit that the cycling champ told his oncologists he had used steroids, growth hormone and erythropoietin.
"When he stood to gain, it appears he was willing to talk about his rich pharmaceutical intake with his doctors," said Art Caplan, a bioethicist at NYU Langone Medical Center. "If he was worried enough to think there might have been a connection, he should have been worried enough to think lot of other people need to know, too."
"I think he owed it to his fans, particularly the young ones that looked up to him and wanted to train like him to say, 'Maybe my use of performance-enhancing drugs had something to do with it,'" Caplan added.
But cancer is a complex problem triggered by a mix of genetic and environmental factors, meaning doping alone was probably not to blame, according to Balar.
"We can never say definitively, but it's highly unlikely," he said.
Balar stressed that the better-known complications of steroid abuse like bone loss, hormone disruption, hypogonadism and mood disorders "are far greater concerns than any potential link with early cancer."
While the cause of Armstrong's cancer may never be known, the consequences of his doping activity and attempts to conceal it are quickly piling up. Five weeks after stepping down from the Livestrong board of directors, Armstrong "expressed his regret" to staff Wednesday and asked that they "stay focused on serving people affected by cancer," according to a statement from the foundation.
Livestrong did not respond to ABC News' request for comment on whether doping might have played a role in Armstrong's cancer, but the charity voiced plans to distance itself from the disgraced athlete in a statement by "charting a strong, independent course forward that is focused on helping people overcome financial, emotional and physical challenges related to cancer."
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