Something Corporate's "Konstantine," penned by singer-songwriter Andrew McMahon, was well-known in the early 2000s Myspace scene as THE heartbreak anthem. The 10-minute, piano-heavy ballad is so intense, McMahon told MTV News he rarely performs it anymore. Despite this, it's not his most challenging song to date — that honor goes to "Caves" by Jack's Mannequin.

You see, McMahon — who started Jack's Mannequin in 2004 after ending Something Corporate — was diagnosed with Acute Lymphatic Leukemia, the most common childhood cancer, at age 22. The band's debut record, Everything in Transit (2005), came out the same day he received a stem cell transplant from his sister.

McMahon made a full recovery, and his experiences in cancer treatment partly inspired The Glass Passenger (2008). He called "Caves," the album's 13th track, the most difficult song he's ever written.

"It was the moment where I said, OK, I'm going to address the fact that I'd gotten sick in the years prior to making this record. I realized that I had been avoiding the subject matter," McMahon explained. "Each verse is like a different scene from the hospital that I was in, and then the end is kind of like this triumphant breaking through to the other side."

The song conveys the same raw, unfiltered emotion that made "Konstantine" so powerful. Its title was inspired by McMahon's rehearsal space, which he rented for cheap thanks to its faulty electricity and ongoing construction.

"It was like working in a war zone. This cave, where it was like mostly dark and sometimes really loud. That's all I did, was just sit in this hole and write the song."

McMahon infamously took his last dose of cancer meds with a shot of Jägermeister, which he says set the tone for the years following his remission.

"I spent my twenties figuring out how to get out from underneath this horrible disease. You start by getting your body better, but nobody prepares you for what it does to your mind," McMahon revealed. "I started partying like fucking crazy."

His struggles motivated him to found the Dear Jack Foundation in 2006, one year after his life-changing stem cell transplant. You can hear more about McMahon's personal journey in the organization's 10th anniversary video.

Dear Jack provides cancer patients with college scholarships, resources, and funds to achieve their dreams. The goal is to "get people out of the hospital and into survivorship in a healthy way," McMahon said.

"We really decided to focus all of our efforts on adolescent and young adult cancer. This is a very, very tricky time to be diagnosed," he continued. "You can just imagine if you get sick and you're in the middle of college, say, trying to get caught back up and be on a trajectory that gets your career started."

The way I see it, hope is the common thread between McMahon's music and philanthropy. Dear Jack gives patients hope in treatment, and McMahon's songs -- "Konstantine," "Caves," you name it -- gives fans hope in, well, life.