Peter Jennings revealed some shocking news Tuesday morning: heís battling lung cancer. The longtime ABC news anchor made the stunning announcement through an Email addressed to his staff.

The Email said in part, "As you all know, this is a challenge. I begin chemotherapy next week. I will continue to do the broadcast. There will be good days and bad, which means that some days I may be cranky and some days really cranky!"

Speculation about Jennings' health first started swirling Monday morning when he did not make the trip to Rome for the pope's funeral. Just hours later, he was diagnosed.

Jennings smoked for years and actually hosted an investigative special on the tobacco industry last fall.

Just a month ago, he hosted a retirement party for friend and fellow anchorman Dan Rather, but today, Rather was unable to put his sorrow into words, saying only that this was a personal matter.

Jennings was on the air last Friday night and is planning to continue working during his treatment, but ABC says it will bring in Charlie Gibson and Elizabeth Vargas to anchor when Jennings cannot.

Today, "Major Dad" star Gerald McRaney, who himself underwent surgery for lung cancer, came to "Extra" with an optimistic message for Jennings: "This is a beatable problem. It's not something that has to overwhelm you. Once you've made up your mind to defeat it, it can be defeated."

Now, even as Jennings readies for this battle, he's intent on easing the shock and worry of friends and loved ones, writing, "Almost 10 million Americans are living with cancer. I am sure I will learn from them how to cope with the facts of life that none of us anticipated."