The 2016 Olympic marathon champion Jemima Sumgong has tested positive for a banned substance in an out-of-competition drug test, the International Association of Athletics Federations announced Thursday.

At the 2012 the first Kenyan woman to win an Olympic marathon, underwent an unannounced test that detected EPO. The test was conducted by the IAAF as part of a program supported by the World Marathon Majors (WMM) organization, the coalition of race organizations that put on the Tokyo, Boston, London, Berlin, Chicago, and New York City marathons.

“We can confirm that an anti-doping rule violation case concerning Jemima Sumgong has commenced this week,” the IAAF said in a written statement first reported by Reuters“The athlete tested positive for EPO following a no-notice test conducted in Kenya. This was part of an enhanced IAAF out-of-competition testing program dedicated to elite marathon runners, which is supported by the Abbott World Marathon Majors group.”

Running in the Cold Nutrition - Weight Lossat an aid station. She was due to defend that title later this month. She placed second at the 2014 New York City Marathon and was runner up at the 2013 Chicago Marathon. At the 2014 Boston Marathon she placed third.

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“While we are distressed to learn of the reports of Jemima Sumgong’s positive drug test, if true, they indicate that we are gaining ground in our long-standing fight against doping,” said Tim Hadzima, general manager of the World Marathon Majors in a written statement. “The Abbott World Marathon Majors is committed to eradicating doping and we will continue to lead the way in introducing and campaigning for aggressive measures.”

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Sumgong’s agent, Federico Rosa, was arrested in July in Kenya, charged with six counts of doping athletes, including alleged involvement with Rita Jeptoo, Sumgong’s former training partner CA Notice at Collection. The charges were eventually dropped, Rosa was released on bail, and he was in Rio for the Olympics. He denied any wrongdoing.

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“We are clean,” she said several times of the runners represented by Rosa.

Shalane Flanagan, who placed sixth at the Rio Games in the marathon, said that the news on Thursday brings up mixed emotions. It came on the same day she officially notified that her 2008 Olympic bronze medal in the 10,000 meters will be upgraded to a silver medal after Elvan Abeylegesse, a Turkish athlete, was given a two-year ban for a steroid despite a late-race fall.

“I’m just floored. It seems like an overwhelming amount of information to process in one day,” Flanagan said. “Unfortunately I’m not surprised, which is the sad part.”

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Flanagan said that Sumgong has directly affected the results of two significant races in her career—the Rio Games and the 2014 Boston Marathon, during which Flanagan led for the majority of the race before finishing sixth in a new American course record of 2:22:02. Jeptoo won that marathon but has since been disqualified. Aleksandra Duliba of Belarus, who placed fifth in the same race, is currently serving a drug ban for a biological passport violation, but her Boston result currently stands. Sumgong is third in the results. 

“Those are two races really high on my priority list and really meaningful to me. It meant years and a lifetime of work to try to achieve something special in those races,” Flanagan said. “It’s really disheartening and I have to be honest—sometimes I ask myself why do I even bother?”

Flanagan admits that the negative feelings ebb and flow—and she’s grateful for the anti-doping efforts officials are making to catch cheats.  

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“I’ve stayed in the sport long enough that I must have more love for it than I do negative feelings. The only answer is that I simply love to run. I’ve only ever wanted to find out how good I could be,” she said. “I could be maybe one of the best in the world—even better than I think—but I’ll never know that for sure. I’ll never retire knowing that full answer, which is a little unsettling. That’s the nature of sport.”

Sumgong will have the opportunity to request a test of a “B” sample. Pending those results, officials will decide if she will serve a ban or be stripped of any titles. She will also have the opportunity to appeal those decisions.

Because Sumgong is currently leading the standings in the WMM rankings, a series champion will not be announced until her appeals process is complete, Hadzima said.

Editor’s note: This story was updated to reflect Flanagan’s upgraded medal will be in the 10,000 meters, not the 5,000.