Trebek wanted to personally share the news about his illness with his fans so they wouldn't be misinformed by "overblown reports" about his health elsewhere.
"Normally, the prognosis for this is not very encouraging, but I'm going to fight this, and I'm going to keep working," Trebek said.
"Truth told, I have to because under the terms of my contract, I have to host Jeopardy for three more years," Trebek joked.
Trebek has hosted the long-running Jeopardy series since 1984, and his contract continues through 2023.
As expected, Trebek's fans showed their support online when the news hit. "One thing I know for a fact: Alex is very aware of how much he means to millions of people, and how we will be pulling for him," one wrote. "I hope that's a comfort."