Transcript for Alex Trebek announces he has stage 4 pancreatic cancer
and we begin tonight with the difficult news from a beloved broadcasting legend. Alex trebek revealing late today he's battling stage four pancreatic cancer. Trebek posting a video message tonight, saying he will fight this, he will keep working, and that he will beat the odds. Trebek has hosted "Jeopardy!" Since 1984 and says he was diagnosed this week. The diagnosis he shares with about 50,000 Americans every year. ABC's Tom llamas tonight with the message from Alex trebek. Hi, everyone. I have some news to share with all of it, and it's in keeping with my long-time policy of being open and transparent with our "Jeopardy!" Fan base. Reporter: Tonight, stunning news from one of the biggest names in television. "Jeopardy!" Host Alex trebek announcing he has stage four pancreatic cancer. On social media, the 78-year-old posting this message to fans. Now, just like 50,000 other people in the United States each year, this week, I was diagnosed with stage four pancreatic cancer. Now, normally, the prognosis for this is not very encouraging, but I am going to fight this, and I am 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. Reporter: Just two weeks ago, trebek was on the road, promoting the 35th season of the and this is the second medical scare in as many years. Last year, trebek took time off the show after a serious fall that required brain surgery. But then he bounced back, at the helm of "Jeopardy!" Just like he's been since 1984. Hosting around 8,000 episodes, a record. Pancreatic cancer has taken the lives of apple CEO Steve jobs, actors Patrick Swayze and Michael Landon and recently, singer Aretha Franklin. But trebek saying tonight he's ready to fight this. Truth told, I have to. Because under the terms of my contract, I have to host "Jeopardy!" For three more years. So, help me. Keep the faith. And we'll win. We'll get it done. And Tom llamas here with us and Tom, Alex trebek's trademark wit on full display there. And we're hearing from some other names wishing him well? Reporter: That's right, David. Friends, family and cog leagues are all wishing him well. Pat Sajak posting this on Twitter. "There is no one I know who is stronger and more determined and I would never bet against him. We and the entire country are pulling for you, Alex." And we are, David. Back to you. All right, Tom llamas, thank of course, we are all pulling for Alex trebek. Let's bring in our chief medical editor Dr. Jen Ashton. We were talking about this pan yatic cancer is one of the most difficult cancers to diagnose. Reporter: This is a rare, but aggressive type of cancer. It's one of the leading causes of cancer deaths. And often, it's not caught until it's at a late stage. The majority of cases are diagnosed when it's already A lot of patients, people at home are going to be wondering, should I ask my doctor if there's a problem there, too? Reporter: There's no screening test, because it's relatively uncommon. But there are risk factors that people can take steps to reduce. Diabetes, obesity, smoking, family history, certain genetic mutations, all increase the risk. But there is reason for hope. There are over 1,000 clinical trials for pancreatic cancer in this country right now, David, and many of them are showing promise. And we are hoping for Alex trebek.
This transcript has been automatically generated and may not be 100% accurate.