The S&P 500 rose 1.4% last week to 1,194.37, marking the sixth consecutive week of gains and a new 18-month high. However, it still remains below its all-time high in the 1,500s, reached in 2007. Upbeat monthly sales for key retailers, coupled with strong auctions for U.S. debt, were among the catalysts ahead of earnings season, which unofficially kicks off today after the close.

Pops and drops
Here are the five biggest S&P 500 increases and five biggest drops of last week (measured Friday close to Friday close):

Winners:

Company

Percent Gain

Eastman Kodak (NYSE: EK)

23.4%

Harley-Davidson (NYSE: HOG)

16%

Wynn Resorts (NYSE: WYNN)

12.6%

American International Group (NYSE: AIG)

11.8%

Washington Post Co. (NYSE: WPO)

10.6%

Source: Capital IQ (a division of Standard & Poor's).

Losers:

Company

Percent Loss

Massey Energy (NYSE: MEE)

(11.9%)

Forest Laboratories (NYSE: FRX)

(10.1%)

Tesoro

(8.3%)

Monster Worldwide

(7.2%)

Aetna

(5.4%)

Source: Capital IQ (a division of Standard & Poor's).

A closer look
Though most corners of the market were bright last week, there were some dark spots. Last week's tragic news about Massey Energy's deadly West Virginia mine explosion has caused the company to shut down the mine. This could cost the coal miner 1.6 million tons in production over the last nine months of the year, or $146 million in revenue, if the production isn't transferred to other mines. However, most production probably can be replaced. The tragedy brings to light hidden risks for investors, too. As my Foolish colleague Alyce Lomax writes, Massey has a history of environmental and safety violations. Massey's story causes investors to rethink the ethics and corporate governance of companies and the associated risks for investment -- not just for Massey, but all companies.

Shares of Forest Labs sputtered last week after the Food & Drug Administration voted against approval of the company's drug Daxas for treating a pulmonary disease commonly known as "smoker's cough," citing safety concerns for side effects. Jefferies & Co. projects the drugmaker lowered its target price on the company to $34 from $42. Both Piper Jaffray and Lazard cut their ratings on the stock.

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Fool contributor Jennifer Schonberger does not own shares of any of the companies mentioned in this article. You can follow her on Twitter. The Motley Fool has a disclosure policy.