It was a tough week for stocks. After eking out gains last week, the U.S. indexes gave up those gains and then some. There was some positive data on the U.S. economy, including lower-than-expected initial unemployment claims, better-than-expected manufacturing numbers from the Empire and Philadelphia Fed reports, and slowing consumer price inflation. However, concerns over Europe's ugly situation overwhelmed investors, and they fled stocks.

The Dow Jones Industrial Average (INDEX: ^DJI) slipped 2.6% during the week, while the broader Russell 3000 shed 2.9%. In particular, investors steered clear of sectors related to economic growth as they sought safety in defensive stocks.

The 3 Worst-Performing Sectors

Russell 3000 Sector

Weekly Price Change

Month-to-Date Price Change

Energy (5%) (5.4%)
Information Technology (4.1%) (2.3%)
Materials (3.7%) (4.8%)

Source: S&P Capital IQ. Weekly price change is Dec. 9-Dec. 16. Monthly price change is Nov. 30-Dec. 16.

Though health care was one of the week's best-performing sectors, all three of the Russell 3000's worst-performing stocks came out of the health-care stable. Shares of biotech developer BioSante Pharmaceuticals (Nasdaq: BPAX), which focuses on products for female sexual health, were decimated after the company's LibiGel failed to deliver a statistically significant boost for female sexual desire when compared with a placebo.

Also ailing after disappointing test results was Endocyte (Nasdaq: ECYT), whose development efforts center on cancer-fighting compounds. Shares were clobbered on Tuesday when results from a phase 2 trial showed that its EC145 therapy didn't help patients with ovarian cancer live longer. The stock shed 65% in a single trading session.

The 3 Worst-Performing Russell 3000 Companies


Weekly Price Change

BioSante Pharmaceuticals (81.8%)
Endocyte (72.2%)
Ampio Pharmaceuticals (Nasdaq: AMPE) (42.9%)

Source: S&P Capital IQ. Weekly price change is Dec. 9-Dec. 16.

Also among the slumping stocks this week were Hyperdynamics (NYSE: HDY) and First Solar (Nasdaq: FSLR). Hyperdynamics is an independent oil and gas driller that could potentially have a big field on its hands offshore the Republic of Guinea. The company has, however, been plagued by operational holdups.

The latest was announced on Wednesday, when the company told investors that "several mechanical and operational issues" had held up the drilling. Hyperdynamics said drilling would resume in 10 days, but investors hammered the stock anyway, taking it down 19% that day.

First Solar, meanwhile, updated its 2011 guidance and provided a forecast for 2012. The company's expectations for 2012 were particularly concerning for investors as the midpoint of the earnings forecast -- $4 per share -- fell well short of the $6.95-per-share target that Wall Street had set. The market took a hatchet to the company's shares, slashing 21% from the share price that day alone.

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