UPDATE 1-Avant shares soar in Pfizer brain-cancer deal

(Adds details on deal, background)

NEW YORK, April 16 (Reuters) - Pfizer Inc (PFE.N) said on Wednesday it had agreed to license from Avant Immunotherapeutics AVAN.O its experimental vaccine to treat the most common form of brain cancer, lifting Avant shares 45 percent in after-hours trading.

"Under the licensing and development agreement, Pfizer will make an upfront payment to Avant of $40 million and will make a $10 million equity investment in Avant," the companies said in a joint press release.

The vaccine, called CDX-110, is now in mid-stage trials. It is designed to coax the immune system to attack the so-called EGFRvIII protein found only in cancer cells, which is believed to stimulate cancer cell growth, the companies said.

The companies said Pfizer, in return for its exclusive worldwide license, will also finance all future costs of developing the product.

In the event CDX-110 and similar Avant vaccines also covered by the deal succeed in clinical trials and reach the market, Avant would be eligible to receive milestone payments of more than $390 million, as well as double-digit percentage royalties on sales.

The deal is slated to close in the second quarter, the companies said.

Despite great potential promise of such therapeutic vaccines, also referred to as immunotherapies, it is a relatively new field and few of them have shown impressive effectiveness in clinical trials.

Pfizer, whose earnings have fallen due to generic competition for some of its biggest drugs, is developing a growing list of cancer drugs in hopes of becoming a major player in oncology. Last month, the company said it was establishing a new separate unit for cancer drugs.

Shares of Avant were trading at $14.50 in after-hours electronic trading, up from their close Wednesday of $10.05 on Nasdaq.

(Reporting by Ransdell Pierson, editing by Richard Chang)