Andrew McMahon was surging to stardom in 2005, but at the same time that his singing career was taking off, he was hit with a leukemia diagnosis. He has since gone on to recover from the disease and now advocates for others suffering from cancer. 

McMahon said that at the time of his diagnosis, his career and fame didn't matter much but that he was focused on his health. "It was a very difficult time, but I think I had amazing support from family and friends," he explained. "When you get sick like that, everything just recedes into the background." He credited his sister's stem cell donation for helping with his fast-tracked recovery. 

Since then, he launched the Dear Jack Foundation that focuses on providing young cancer patients with programs that can help improve their quality of life. McMahon said he realized that some charities he had been working with weren't meeting the needs of the adolescents and young adults so he ended up taking matters into his own hands.

"Part of the reason is that we focus on this young adult bracket, which is 15 to 39 years of age, is that it is a particularly tricky time to go through this," he said.