UPDATE 1-Dendreon shares tumble ahead of key prostate data

* Data on prostate cancer vaccine due on Tuesday

* Shares tank 45 pct after rising as much as 14.4 percent

NEW YORK, April 28 (Reuters) - Trading in shares of biotechnology company Dendreon Corp (DNDN.O: Quote, Profile, Research) were halted on Tuesday after falling 45 percent ahead of major data scheduled to be released later in the day on its experimental prostate cancer vaccine.

Shares fell $9.74 to $11.81 in early afternoon trading on the Nasdaq before the exchange halted trading. Earlier in the day, the shares rose as high as $24.67 in heavy dealings.

The company was not available to comment.

Full results of a late-stage clinical trial involving the company's Provenge vaccine were being released Tuesday at the American Urological Association annual meeting in Chicago.

It has been a volatile few weeks in Dendreon shares, to say the least. The stock, which traded at a low of $2.55 in March, soared earlier this month when the company said the trial, known as IMPACT, had reached the main study goal. The data bolstered chances that Provenge would become the first approved therapeutic vaccine for any type of cancer.

Unlike traditional vaccines that prevent disease, Provenge treats it by stimulating the body's own immune system. (Reporting by Lewis Krauskopf; Editing by Derek Caney and Gerald E. McCormick)