Biotech sees best day since late June

Traders work on the floor of the New York Stock Exchange shortly after the opening bell in New York.
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Traders work on the floor of the New York Stock Exchange shortly after the opening bell in New York.

The iShares Nasdaq Biotechnology ETF (IBB) gained 3 percent on Monday, its best day since late June.

Some of the fund's top holdings like Vertex Pharmaceuticals, Amgen and Shire gained more than 3 percent in intraday trading, driving it higher.

The sector also saw gains after Horizon Pharmaceuticals announced it will acquire Raptor Pharmaceuticals for $9 per share, roughly a 20 percent premium to Raptor's Friday closing price of $7.45.

Horizon CEO Timothy Walbert said that the acquisition will help boost the company's rare disease revenue as it looks to expand its business in the segment.

Raptor shares surged 20 percent in intraday trade, while Horizon shares jumped more than 9 percent.

Even with Monday's gains, the IBB is still down 19 percent in the past year.