UPDATE 3-Cephalon CEO dies at 57 while on medical leave

* Frank Baldino Jr. was company founder

* Cephalon says no transition announcements yet (Adds comment from analysts)

BOSTON, Dec 17 (Reuters) - Frank Baldino Jr., chief executive and founder of biotechnology company Cephalon Inc CEPH.O, died Thursday night at the age of 57, the company said. The cause of death was not disclosed.

Cephalon announced in August that Baldino would take a temporary medical leave and said the company, which makes the sleep disorder drugs Provigil and Nuvigil, would be run in his absence by Kevin Buchi, its chief operating officer.

On Dec. 6 the company said Baldino would be on medical leave indefinitely and that Buchi would continue to perform his duties.

Announcing his death, Fritz Bittenbender, vice president of public affairs, said that “in deference to Frank and his leadership, we are not going to make any announcements about the transition in the near future.”

Baldino, who received a PhD in pharmacology from Temple University, founded Cephalon in 1987 and built it on the back of Provigil, a drug for a rare sleep disorder called narcolepsy. Provigil was subsequently approved in other indications.

The company now focuses on central nervous system disorders and on cancer. Cephalon has a market value of $4.7 billion.

Few biotech CEOs are as identified with the companies they run as Baldino.

“This guy would run through a brick wall for his company,” said Eric Schmidt, an analyst at Cowen and Company who has covered the company and known Baldino for 15 years. “He was one of the toughest people I have ever met.”

Baldino could be prickly if challenged, and his relationship with federal regulators was not always smooth.

In 2008 the company agreed to pay $425 million to settle allegations it marketed three drugs for uses for which they were not approved; and the Federal Trade Commission has challenged the legality of its deals with four generic drugmakers aimed at delaying entry to the U.S. market of cheaper versions of Provigil.

But Baldino continued to drive the company’s growth, often using novel financing techniques to license products or make acquisitions.

“Without Frank they have lost the soul of the company,” said Louise Chen, an analyst at Collins Stewart. “I think it makes it more likely that Cephalon will be put up for sale.”

From 1981 to 1987, Baldino served as senior research biologist in the medical products department at DuPont Co DD.N, where he was responsible for developing research strategies for identifying novel neuropharmaceutical agents.

Among many other positions, Baldino chaired the Executive Council of the Harvard Division of Sleep Medicine and was a member of the boards of Temple University, the University of the Sciences in Philadelphia, and the Franklin Institute. (Reporting by Toni Clarke, editing by Gerald E. McCormick, John Wallace, Phil Berlowitz)