Last week, YouTuber, New York Times bestselling writer and science educator Hank Green announced that he had been diagnosed with Hodgkin lymphoma, a treatable form of blood cancer that affects the lymph system, according to a CNN article. The announcement was made via a video posted to the “vlogbrothers” YouTube channel that he hosts with his brother, fellow New York Times bestselling author John Green.

Shortly before his diagnosis, Green, 43, said he noticed that his lymph nodes were enlarged and there was swelling in his armpit. A subsequent biopsy confirmed he had Hodgkin lymphoma. In the description for the video, Green explained that by the time the YouTube video went live, he had already started his first round of chemotherapy. He also explained that the cancer is very treatable and “the goal is cure.”

“I’m not really looking forward to it, but I’m looking forward to starting on the path,” he said in the 13-minute video, which has already been viewed 7 million times.

Green said multiple risk factors—including medications, an autoimmune condition and having had mononucleosis as a child—might have contributed to his diagnosis.

Cancer Health’s Basics on Lymphoma explains that lymphoma occurs when white blood cells of the immune system grow out of control. There are two main types, Hodgkin lymphoma and non-Hodgkin lymphoma, each of which has multiple subtypes.

In Hodgkin lymphoma, large abnormal lymphocytes (usually B cells) build up in the lymph nodes. Most people in developed countries have what is known as the classic type. It typically starts in lymph nodes in the chest, armpits or neck. It may spread through lymph vessels to other lymph nodes, but it usually does not spread elsewhere in the body.

It generally responds well to treatment and can often be cured. In fact, the American Cancer Society estimated about 8,830 new cases of Hodgkin lymphoma in the United States in 2023, with a five-year relative survival rate of 89% for all diagnosed patients.

Green, who teaches history, science, math and more via easy-to-digest YouTube videos, has used his diagnosis to continue to educate.

“People say that chemo ‘poisons the whole body to poison the cancer’ but this kinda misunderstands the situation. Cancer cells are different…they grow and use resources differently. Chemo drugs use those differences to poison cancer cells /dramatically more/ than healthy cells,” he tweeted recently.

“All of the time that I have spent investing in friendships—and even when they have been hard, to try and keep them strong, and even when I have been busy, to try and spend time with them—has been joyful in the moment and wise in the long term,” Green said in the video. “I’ve really needed friends in the last few weeks, and I’ve been very grateful to have them.”