The stock surged about 283%, or about $167, since the opening bell.
At least one hedge fund is probably really pleased with this investment.
The largest shareholder of Puma Biotechnology is Adage Capital Management, a Boston-based hedge fund founded by Phil Gross and Robert Atchinson.
According to the latest 13F data, Adage last held 5,686,668 shares. That means they have made about $950 million on the position since the opening bell today.
Adage first reported its position in Puma Biotechnology on December 31, 2012. The fund held about 5.2 million shares then. From that time until yesterday's market close, shares of Puma Biotechnology have risen 214%.
And all those who sold out of the position before this news broke are probably kicking themselves right about now.