David Urdal, the scientific entrepreneur who co-founded Dendreon 15 years ago and helped turn it into a pioneer of cancer immunotherapy, is stepping down from his job as chief scientific officer at the Seattle biotech company, according to Xconomy Seattle.

Urdal, 61, will retire as Dendreon’s executive vice president and chief scientist at the end of 2011, according to a regulatory filing with the Securities & Exchange Commission. He will officially hand over his duties to Mark Frohlich, chief medical officer, on Dec. 31.

Urdal made the announcement to his colleagues in-house via e-mail: “Anyone who has talked to me for more than two minutes knows that I have become bewitched, bewildered and bedazzled with the arrival of our first grandchild last April. The same month that the FDA brought us into a new era of cancer treatment with the approval of Provenge, my daughter brought the Urdal family into the next generation with the birth of my granddaughter. I look forward to seeing the world through her eyes and the eyes of the grandson we expect to see in June.”

“I am now in my sixteenth year with Dendreon and what an extraordinary journey it has been—the first autologous cellular immunotherapy approved by the FDA! What an achievement and what a pleasure it is to be a member of such a truly extraordinary team—the Dendreon team—as we won the high achievement of Provenge approval. We are just getting started.”

Dendreon CEO Mitch Gold, in his note to employees, said: “Dave has been an inspiration to so many of us, myself included. Over his many dedicated years, he has provided thoughtful leadership, helping to guide us from inception through the FDA approval of the world’s first autologous cellular immunotherapy.”

The company, which now employs about 1,500 people around the country, is worth almost $5 billion, and has a drug that could generate more than $4 billion in annual worldwide sales at its peak, according to JP Morgan analyst Cory Kasimov.