Canadian "Jeopardy!" host Alex Trebek announced he's been diagnosed with advanced pancreatic cancer in a YouTube video on Wednesday that had a positive tone despite the grim prognosis.

"Just like 50,000 other people in the United States each year, this week I was diagnosed with Stage 4 pancreatic cancer," Trebek said in the message posted on the "Jeopardy!" YouTube channel.

"Now, normally the prognosis for this is not very encouraging. But, I'm going to fight this and I'm going to keep working. And with the love and support of my family and friends, and with the help of your prayers also, I plan to beat the low survival rate statistics for this disease.

"Truth told -- I have to, because under the terms of my contract, I have to host 'Jeopardy!' for three more years," the 78-year-old continued, wearing a signature suit on the "Jeopardy!" set and employing the wry wit he has brought to the hit quiz show for decades.

"So help me: keep the faith and we'll win. We'll get it done. Thank you."

Born in Sudbury, Ont., Trebek attended the University of Ottawa and hosted a number of CBC TV programs early in his career, including the high school quiz show "Reach for the Top."

He moved to the United States in the 1970s and became an American citizen in 1998. He and his wife, Jean Currivan, have two children.

Trebek has won several Emmy Awards for hosting "Jeopardy!" since 1984. With a matter-of-fact delivery style and genial personality, the role has made him a worldwide star and the subject of spoofs on "Saturday Night Live."

Trebek received the Order of Canada medal in 2017 in recognition of his "iconic television work" and commitment to educational, environmental and humanitarian causes.

In late 2017, "Jeopardy!" went on hiatus after Trebek underwent surgery for blood clots on his brain caused by a fall.

Several months after the surgery, he appeared in a video on the show's Facebook page, wearing a "Jeopardy!" baseball cap. Using the same tone he employs to explain difficult subjects on the show, the unflappable Trebek said: "I had a slight medical problem, subdural hematoma, blood clots on the brain caused by a fall I endured about two months ago."

In 2007, he was hospitalized for about a week after suffering what was described as a minor heart attack.

Sharing his cancer diagnosis was "in keeping with my longtime policy of being open and transparent with our 'Jeopardy!' fanbase," Trebek said.

"I also wanted to prevent you from reading or hearing some overblown or inaccurate reports regarding my health. So therefore, I wanted to be the one to pass along this information."

Social media was flooded with tributes for Trebek after his announcement.

Former Ontario premier Bob Rae shared his sympathies on Twitter, calling Trebek a "very fine man."

Ken Jennings, who holds the record for the longest winning streak on "Jeopardy!," tweeted that he hopes Trebek finds comfort in the millions of fans who are rooting for him, warning L.A. oncologists that they better prepare themselves to have their pronunciations corrected.

"Alex Trebek is in a way the last (Walter) Cronkite: authoritative, reassuring TV voice you hear every night, almost to the point of ritual," he tweeted, referring to the late broadcaster known as the "most trusted man in America."

Singer-songwriter Ron Sexsmith also sent his positive thoughts to the "great Canadian" via social media.

-- With files from Adina Bresge, David Friend and the Associated Press