Peter Jennings has lung cancer. The longtime ABC News anchor plans to keep appearing on ''World News Tonight'' as he undergoes chemotherapy

Credit: Peter Jennings: Nancy Kaszerman/ZUMA Press

Peter Jennings, last of the Big Three news anchors, has seen rivals Tom Brokaw and Dan Rather step down in recent months, but he’s vowing to remain on the air as long as he can, even after being diagnosed Monday with lung cancer. Jennings, who’s been the sole anchor of ABC’s World News Tonight since 1983, wrote an e-mail message Tuesday to fellow ABC News staffers, saying that, though he begins 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!” He added, ”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.”

ABC News President David Westin told staffers in an e-mail that Charles Gibson, Elizabeth Vargas, and others would fill in for Jennings as needed. Already, the ailing anchor has missed one big story; it was Charles Woodruff who anchored the network’s coverage of the death of Pope John Paul II over the weekend. ”Peter’s been given a tough assignment,” Westin wrote. ”He’s already bringing to this new challenge the courage and strength we’ve seen so often in his reporting from the field and in anchoring ABC News.”