Shares of Medarex Inc. (MEDX) surged Monday on news that two patients taking the biopharmaceutical company's prostate cancer treatment in a mid-stage trial are now cancer free.

The Mayo Clinic announced Friday that two men being treated with Medarex's Ipilimumab, along with a standardized hormone treatment and radiation therapy, experienced a reduction in tumor size, allowing them to be treated with surgery.

The patients, who had previously been considered inoperable, are part of a Phase II study involving 108 patients. In both cases, the aggressive tumors had grown well beyond the prostate into the abdominal areas, the Mayo Clinic said.

Shares of Medarex surged 17% to $8.63 in recent trading, after earlier rising as high as $9.01. The stock is approaching its 52-week high of $10.12, which it set last August.

"This is one of the holy grails of prostate cancer research," Eugene Kwon, a Mayo Clinic urologist and leader of the clinical trial, said. "We've been looking for this for years."

The Mayo Clinic is the largest non-profit group practice in the world.