NEW YORK, July 28 (Reuters) - U.S. stock index futures dropped to session lows on Tuesday as several companies, including Office Depot Inc, posted lackluster quarterly results and investors turned cautious ahead of key reports on home prices and consumer confidence.
* S&P 500 futures were 7.10 points lower and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures shed 48 points, and Nasdaq 100 futures dipped 5.25 points.
* Although the primary focus remains on second-quarter earnings, investors are eager for economic data, including Tuesday's Standard & Poor's/Case Shiller home price indexes, to provide further evidence of a recovering U.S. economy to justify a further run-up in stocks.
* The benchmark S&P 500 has rallied 45 percent from the 12-year closing low of March 9.