Mark – who sings and plays bass guitar in the rock band – shared the news with fans on his Twitter page on Wednesday night.
He explained: “For the past three months I’ve been undergoing chemotherapy for cancer. 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.”
The 49-year-old said that he still has “months of treatment ahead”, but insisted he’s trying to retain a “hopeful and positive” attitude.
“Can’t wait to be cancer free and see you all at a concert in the near future,” he added. “Love to you all.”
He also posted a photo of himself in a hospital waiting room on his Instagram story, joking: “Yes hello. One cancer treatment, please.”
Bandmate Tom DeLonge tweeted later: “I too, have been aware of [Mark’s] cancer diagnosis for awhile now.
“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.”
Drummer Travis Barker posted a picture of himself and Mark on his Instagram story, writing: “Love you @MarkHoppus.”
Mark has been with Blink-182 since the trio broke into the mainstream in the 1990s with their hit All The Small Things.
Over the years, the band has racked up a number of UK top 20 singles including What’s My Age Again?, The Rock Show and the ballad I Miss You.
In 2017, they were nominated for their first Grammy for the album California.