Hoppus, 49, shared his diagnosis Wednesday on Twitter, revealing that he has been undergoing chemotherapy treatment.
"For the past three months, I've been undergoing chemotherapy for cancer," he wrote. "I have cancer. It sucks and I'm scared, and at the same time I'm blessed with incredible doctors and family and friends to get me through this. I still have months of treatment ahead of me but I'm trying to remain hopeful and positive. Can't wait to be cancer free and see you all at a concert in the near future. Love to you all."
Kevin Winter/Getty Images Mark Hoppus in 2018
Well wishes for the rocker began pouring in immediately.
"My heart hurts so much," one fan replied. "Praying for you, Mark. Kick cancer's ass."
"So many people you've never met are pulling for you," wrote another. "We love you Mark!"
"We love you Mark," the brand Hot Topic tweeted. "You got this!"
"Lots of love to you Mark," wrote Billy Martin, of Blink-182 peers Good Charlotte.
"Hope you kick it's ass soon," wrote former KROQ and current KLOS DJ Kevin Ryder.
The band, which previously featured Tom DeLonge, has earned a host of platinum records on the back of infectious tunes. Take Off Your Pants and Jacket went double platinum (2 million sales) in 2002, Enema of the State went five times platinum in 2001, and their self-titled album was awarded platinum status in 2004.