Stocks opened modestly lower on Wall Street Tuesday after a survey showed home prices in major cities dropped for the second straight month in October, raising concerns about the shaky housing market.

The Standard & Poor's/Case-Shiller index released Tuesday showed prices dropped in October from September in 19 of the 20 cities tracked.

Prices in a majority of cities declined for the second straight month, reflecting the typically fall slowdown after the peak buying season. Prior to that, prices had risen for five consecutive months in at least half of the cities tracked.

The S&P 500 has risen for four straight sessions and turned positive for the year on Friday, with improving economic data helping to boost equities last week. The gains, which lifted the benchmark index above its 200-day moving average, were amplified by the light pre-holiday trading.

"There won't be much action today because of the holiday, but if there's anything surprising in the data we could see an exaggerated move because of how light the volume will be," said Scott Brown, chief economist at Raymond James in St. Petersburg, Florida.

The data comes after better-than-expected housing and jobless claims data last week that confirmed a slowly improving economy.

Going into 2011's last week of trading, the Dow is up 6.2 percent so far this year, the S&P is up less than 1 percent and the Nasdaq is down 1.3 percent.

Markets were flat globally following the long Christmas weekend, with European stocks nearly flat.

Sears Holdings Corp plans to close 100-120 Kmart and Sears stores and sees its adjusted fourth-quarter earnings before interest, taxes, depreciation and amortization falling by more than half from a year ago. Shares dropped 17 percent to $38 before the bell.

Reuters and The Associated Press contributed to this report.