In 2009, the American Idol winner served as grand marshal for the Race For Hope, which benefits the National Brain Tumor Society and Accelerate Brain Cancer Cure, despite his brother's passing just one day before.
Returning to the annual 5K in Washington, D.C., on Sunday, Cook tells PEOPLE, "I came back because the cause is important to me and my family, as well as countless others. Brain tumors and brain cancer continues to be one of the most under-funded diseases."
So the singer made sure to do his part, raising $140,000 with his team and fans as part of the $2.3 million the race earned overall.
"To be able to take this time to honor my brother and everyone who is affected by cancer is huge for me," says Cook, who chatted with other race participants as they completed the 3.1 mile course. "It's a great way to help continue the fight Adam started almost 12 years ago."
And he didn't just make a quick appearance at the race either. In addition to running it ("I'm still in the 'as long as I finish' mode," he jokes of his time goal) Cook came in early to play in a charity golf event on Friday and stayed late, taking photos with every survivor at the race.
"The last year has been a process," says the singer of coping with his brother's death. "It's all about perspective and remembering what Adam went through so we can work to help avoid anyone else having to do the same."
For more information about the charity, visit curebraintumors.org.
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