Hank Green, a novelist and longtime host of quirky YouTube educational videos, announced on Friday that he was recently diagnosed with Hodgkin’s lymphoma, a form of cancer.
“Good news and bad news. One, it’s cancer,” he said in a video on his YouTube channel, Vlogbrothers. “Good news, it’s something called Hodgkin’s lymphoma,” he added. “It’s one of the most treatable cancers. It responds very well to treatment.”
Mr. Green first started Vlogbrothers in 2007 with his older brother, John Green, the best-selling author of young adult novels, including “The Fault in Our Stars” and “Paper Towns.”
Hank Green’s debut novel, “An Absolutely Remarkable Thing,” was a best seller inspired by having achieved internet fame and experiencing the anxiety and awkwardness it can bring.
“In a lot of ways it comes from a lot of my personal experience with how success feels,” he said in a 2018 interview. “There’s the very weird feeling of being bigger in people’s heads than you feel you are.”
Over the past decade, the Green brothers have built an online video empire with more than 10 YouTube channels, like “SciShow” and “Crash Course,” with more than 20 million subscribers combined and even more millions of views.
Hank Green, who is no stranger to explaining scientific matters to his followers, said he first suspected something might be wrong when his armpit swelled unusually. Then, he noticed he had enlarged lymph nodes.
He went to a doctor for scans, an ultrasound and, later, a biopsy. He was aware that he had risk factors for lymphoma, including an autoimmune disease and having had mono, or infectious mononucleosis, as a child.
He said he wasn’t certain how his treatment would affect making videos, but he was confident that his online community would understand.
On TikTok, where Mr. Green has 7.5 million followers, he guessed he might spend more time writing his newsletter, “Nerdfighteria,” depending on how he is feeling throughout the process.
“I know I’m going to feel like garbage,” he said. “It’s going to be really unpleasant.”
Mr. Green said he began his first round of chemotherapy on Friday, which will continue for at least four months.
He recounted a conversation he had with his brother, John, in the video, saying he told him he thought “this is the best time so far in human history to get lymphoma.”
“And you gave me a very John Green thought: ‘Well, a year from now would’ve been better,’” he recalled with a laugh.
The brothers also co-founded VidCon, an internet culture convention hosted annually in Anaheim, Calif.
VidCon said on Instagram that Hank Green would not be attending the convention, which is scheduled for next month.
“To our Co-Founder, go-to science guy, and only person on the internet who seems to understand where all the candle wax goes: we’re sending all the love from the VidCon community & beyond,” it said in a statement.
Fans of Mr. Green also shared messages of support in the comments of his videos and across social media on Friday, including sending pictures of pelicans, at his very specific request.
For now, Mr. Green said his main symptom is stress, as he fears a cancer diagnosis poses the threat of hijacking his identity.
“I want to be fun, goofy science guy,” he said, “not struggling with anxiety, cancer guy.”