Boys under 11 can now participate in the Race for Life after a mother's petition to allow her seven-year-old son to run beside her prompted Cancer Research UK to change its rules of registration.
Claire Parker launched the petition in dismay when her son was refused entry onto this summer's race in Chesterfield. It received 57 signatures.
Emma Hyatt, head of Race for Life, said in a statement: "It's wonderful that people feel so passionately about Race for Life and we take responsibility for listening to their views very seriously.
"We have listened to Claire Parker and gained further feedback from a range of supporters to gauge their feelings on the subject. As a result we have decided the age limit of 11 and under for boys taking part in 2012, which we trialled for the first time last year."
A spokewoman for the charity advised that the decision was predominantly as a result of the feedback from other supporters, who could not be named "for obvious reasons".
However, Parker, who will now be able to run side-by-side with her son Connor, said that she was "over the moon" about the decision. In a statement to the Derbyshire Times, she said: "When I was battling lymphoma, [Connor] was such a massive source of strength - he went through everything with me and I'm delighted we'll be able to cross that finishing line together."
But she added that "realistically I would love Race for Life to be open to everyone as everyone suffers from cancer".
The Race for Life series launched in 1994 and is a women-only fundraising event series. It has remained so, Cancer Research says "due to its huge popularity and non-competitive atmosphere which encourages women of all ages and fitness levels to take part".
Last year, however, low sign-ups forced the cancellation and merger of several Race for Life events. This was despite Tesco coming on board as corporate supporter and pledging to bring one million more runners to the series.