Conservative radio talk show host Rush Limbaugh announced on Monday that he has been diagnosed with "advanced lung cancer" but plans to continue to do his program "as normally and as competently" as he can while he undergoes treatment.Limbaugh, 69, said on the air he first realized something was wrong over the weekend of his January 12 birthday, after he began experiencing shortness of breath. He said his diagnosis was confirmed on January 20 by two medical institutions. Otherwise, Limbaugh told his listeners, he was for the moment "experiencing zero symptoms."A mainstay of US talk radio and the culture wars for more than 30 years, Limbaugh said he would be absent from the broadcast for "the next couple of days as we figure out the treatment course of action and have further testing done.""But as I said, I'm going to be here as often as I can," he added. He said he hoped to return to the airwaves on Thursday.The radio host began his announcement expressing discomfort at talking about himself, then went on to say: "I have to tell you something today that I wish I didn't have to tell you.""The upshot is that I have been diagnosed with advanced lung cancer," he said. The shortness of breath he had thought might have been asthma turned out, he said, to be "a pulmonary problem involving malignancy." He made no mention of a prognosis.Limbaugh has been a leading voice of the political right and a nemesis of the left since launching his show in 1985 amid the Republican revolution of Ronald Reagan, a man he has called "the greatest president of the 20th century."Espousing a provocative, populist brand of social and political conservatism, Limbaugh has commanded a weekly audience of about 20 million listeners - he calls them "ditto heads" - during a three-hour daily broadcast airing on some 600 radio stations across the United States.Detractors such as liberal former Senator Al Franken - a onetime comedian who wrote a book titled "Rush Limbaugh is a Big Fat Liar" - have criticized him as a divisive figure who routinely distorts the facts.Still, Limbaugh's success helped shape the Republican party's agenda in the media and spawn a wave of conservative commentators on radio, television and the internet, among them Bill O'Reilly, Sean Hannity, Glenn Beck and Alex Jones.Much of Limbaugh's appeal has been attributed to his brash, colorful style, and his delight in baiting liberals.He coined the term "femi-Nazis" to disparage women's rights groups and once said the "difference between Los Angeles and yogurt is that yogurt comes with less fruit."Limbaugh has experienced a variety of medical problems over the past couple of decades, including a loss of hearing reversed by a cochlear implant, as well as an addiction to prescription painkillers that landed him in rehab for several weeks in 2003.