The mammoth event was organized at about 25 venues across the UK, including Stormont estate.
Before the race started 15,000 runners nationwide warmed-up with stretching exercises in an attempt to set a Guinness world record for the 'largest simultaneous stretch'.
Rachel Roxburgh, head of Race for Life, said: 'This is the first time that Cancer Research UK has attempted a Guinness world record and the very fact that we are able to is testament to the thousands of women that year on year support us.'
'We hope that this race will not only help us reach our fundraising target of Ł46m, but that it will be remembered for years to come as the day that women everywhere came together to help beat cancer .'
Craig Glenday, editor of the Guinness Book of World Records said that they were thrilled when Cancer Research UK came to them with this record attempt.
