London Marathon chief executive Nick Bitel has criticised world governing body the IAAF and said race organisers are "very concerned" by claims in the Sunday Times that seven winners in a 12-year period recorded suspicious blood scores.
The newspaper has published fresh allegations following its analysis of drugs test data from 2001 to 2012.
It said the winners of 34 major marathons around the world - one in four - during the period should have faced censure or investigation because of their test results, with those athletes collecting more than £3million in prize money.
London was the worst affected, with seven wins, six second places and seven third places out of 24 men's and women's races allegedly involving suspicious blood scores.
"We believe there are people in our sport who are cheating and everyone has a part to play to protect those who are not," Bitel said in a statement.
"We continue to be at the forefront of anti-doping measures for marathon runners as we are determined to make marathon running a safe haven from doping but we cannot do it all on our own and rely heavily on the IAAF.
"We are therefore very concerned by the allegations made in the Sunday Times today and we will be discussing the implications of the allegations with the IAAF."
Appearing on BBC Radio Five Live's Sportsweek programme, Bitel criticised the IAAF, saying that although the Marathon pays for its own drugs testing, it does not administer the program and does not get to see the results, meaning organisers had been unaware of the suspicious blood data.
"We are disappointed," he said. "We're doing more than anybody else to fight doping in our sport. We were the first people to call for blood testing and in fact we're still probably the only event in the world that blood tests all our athletes.
"What this story is really about is the IAAF's failure to take effective action. Those athletes that have been caught... have only been caught because of the tests at the London Marathon. The IAAF needs to do more to stop people from starting (a race) that have blood values that are out of normal range.
"What is concerning is that we're never told these results even though we're paying tens of thousands of pounds to get these athletes tested."
Not all of the tests studied by the Sunday Times were taken at the time of the marathons in question.
According to the newspaper, the athletes involved collected more than £3million in prize money for their results.
London Marathon organisers have vowed to take legal action to recover prize money awarded to Russia's Liliya Shobukhova, whose competitive results as of October 9, 2009 have been disqualified by the IAAF.
Shobukhova finished first and second, respectively, in the 2010 and 2011 London Marathons, and had been the second fastest female marathon runner of all time behind Paula Radcliffe before receiving a two-year doping ban from Russia's athletics federation in 2014.