Bearish option volume was unusually heavy on Dendreon Corporation (NASDAQ:DNDN - 6.21) last Friday, with more than 6,300 put contracts crossing the tape. By contrast, the biotech stock typically sees fewer than 2,000 put options change hands during the course of an average session. Taking a closer look at the day's volume, it looks as though most put players took a short-term approach by trading DNDN's weekly options.

Specifically, the day's most active strike was the weekly 1/11 6.50-strike put, where 1,886 contracts were exchanged. Most of these contracts traded near the ask price, suggesting they were purchased, and open interest at this strike rose over the weekend by 1,793 contracts. In other words, it looks like new short-term puts were bought to open on DNDN last Friday.

These soon-to-expire options traded at a volume-weighted average price (VWAP) of $0.65, which means put buyers need DNDN to drop below breakeven at $5.85 (strike price minus VWAP) before the end of this week.

However, it looks like those bearish bets were ill-timed. DNDN is up more than 3% at last check after the Provenge parent announced preliminary fourth-quarter revenue of $81.6 million, on an adjusted basis. Analysts, meanwhile, had anticipated quarterly sales of just $80.8 million.