The coronavirus outbreak has forced Cancer Research UK to cancel all of its almost 400 Race for Life events that were due to take place this year.
The charity, which had hoped to postpone the events in the Race for Life series until autumn, is urging supporters to take part in Race for Life at Home to raise funds instead.
In 2018/19, the charity raised £35m through Race for Life, which normally consists of 5km, 10km and muddy obstacle course events that participants are sponsored to take part in.
Race for Life at Home encourages people to put their own spin on the fundraising initiative, including the option to embark on a month-long fitness challenge.
Supporters can also opt to do a 5km or 10km run (or walk), or come up with their own challenges and share them with #RaceForLifeAtHome.
A spokeswoman for Cancer Research said Race for Life at Home had raised more than £100,000 so far.
Cancer Research, which closed 600 of its shops across the UK on 20 March, expects to lose up to a quarter of its income from fundraising this year.
Michelle Mitchell, chief executive of Cancer Research, said: "Covid-19 has unfortunately impacted our plans and we’ve made the difficult decision to cancel our Race for Life events.
"We’re sorry for our participants and volunteers who hoped to join in this year, but we hope they will understand that safety must be the priority.
"We’re urging people to sign up to Race for Life at Home and join our amazing Race for Life community."