The date for one of Philadelphia's most popular races has been pushed back due to Pope Francis' upcoming visit to the city.
The American Association for Cancer Research Rock 'n' Roll Philadelphia Half Marathon will take place on Halloween -- Saturday, October 31 -- this year, race organizers confirm to NBC10.
The 38-year-old race that features live bands along the route and a concert at the finish line traditionally takes place on the third Sunday in September. But this year, that's two days before the start of the World Meeting of Families conference and a week before Pope Francis' celebration of mass on the Benjamin Franklin Parkway.
Some 2 million people are expected to flood the city to take part in the mass and get a glimpse at the popular pontiff. The visit is being hailed as the largest event in Philadelphia's modern history.
Race organizers say they've been working with city officials to find a new weekend for the 13.1 mile run.
"We have been in constant communication and cooperation with the City of Philadelphia, Parks & Recreation and all other involved agencies to secure an amicable race day for 2015," Josh Furlow, Executive Vice President of Global Events for the Rock 'n' Roll Half-Marathon Series said in a statement.
A source with knowledge of the situation said a lack of hotel rooms were one problem area for holding the race on it's traditional weekend. NBC10 previously reported many hotels in and around the city have blacked out rooms in anticipation of the Catholic conference and pope's visit.
Registration will open Thursday on the race's website. The first 1,000 entrants will pay a discounted fee of $55, organizers said.
The Rock 'n' Roll Health & Fitness Expo will take place on Thursday, Oct. 29 and Friday, Oct. 30 at the Pennsylvania Convention Center.
The date change isn't the only new thing for this year's race. For the first time, it has a title sponsor in the American Association for Cancer Research -- the world's largest scientific organization focused on cancer research.