Olympic champion Jemima Sumgong will not defend her London Marathon title after failing a drugs test in February.
The Kenyan, who became her country's first female Olympic marathon champion when she triumphed in Rio de Janeiro last year, tested positive for banned substance EPO in an out-of-competition test carried out by the IAAF.
"We are extremely disappointed to learn that Jemima Sumgong failed an out of competition drugs test in February," said London Marathon Events chief executive Nick Bitel.
"She is currently suspended from competition pending the B test and the outcome of the investigation.
"Sumgong will therefore not run in London on 23 April to defend the title she won last year."
Kenya was declared "non-compliant" by the World Anti-Doping Agency last year but was reinstated in time for the Rio Games.
More than 40 Kenyan track-and-field athletes have failed doping tests since 2011.