S&P Add Sweet for Celgene

Word that Standard & Poor's will add Celgene (CELG Quote) to its S&P 500 index was lifting the biotech company's stock Tuesday.

Lately, Celgene was up 6% to $52.80. Shares of companies added to the S&P 500 often rise because fund managers who track the index have to own the stock.

Celgene is set to replace AmSouth Bancorp (ASO Quote), which is being acquired by Regions Financial(RF Quote) in a deal expected to close by Nov. 6.

Regions, in turn, will supplant RadioShack (RSH Quote) in the S&P 100, Standard & Poor's said Monday.

RadioShack, with a market capitalization of about $2.4 billion, ranked 100th in the S&P 100 as of the previous close of trading. The moves will occur after the close of trading Nov. 3.