"I will be with him every step of the way on stage and off," said Barker.
Mark Hoppus' Blink-182 brothers have his back amid his battle with cancer.
The bassist revealed his diagnosis on Wednesday, sharing a statement to his Instagram Story, followed by a photo of him getting chemotherapy. "Yes hello. One cancer treatment, please," he captioned the image.
In his initial post, he confirmed he has been undergoing treatment for the past three months.
"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," he wrote. "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."
That love was given right back to him from his friends and fans, with many of them taking to social media to share their support for him through his fight.
"Love you," Travis Barker captioned a throwback photo of the two on his Instagram Story, before releasing a statement to E! reading, "Mark is my brother and I love and support him. I will be with him every step of the way on stage and off and can't wait for us to play together again soon."
Former Blink-182 vocalist Tom DeLonge also shared a post about Hoppus to Twitter.
"I too, have been aware of @markhoppus's cancer diagnosis for awhile now," he tweeted. "And to add to his own words that he used today, I would also like to say that he is strong, and a super-human who is pushing through this difficult obstacle with a wide-open heart."
He also added the hashtag #WeHaveHisBack.
Among the many sending messages of support to Hoppus were "The Office" alum BJ Novak, MTV's Dave Holmes, members of Good Charlotte, Yellowcard and Taking Back Sunday, as well as the official accounts for Hot Topic, Eve 6 and Jimmy Eat World.
❤️ you’re on our minds, Mark. Your attitude is going to be magnified by so many people.