Shares of Amgen Inc. fell nearly 4 percent Thursday after the biotech giant said it had received an inquiry from U.S. regulators about a delay in the release of negative study results about its blockbuster anemia drug Aranesp.

The Security and Exchange Commission’s Atlanta District Office asked Amgen to provide information and documents about the study, the Thousand Oaks-based company said in a regulatory filing Wednesday.

The request relates to a study by Danish researchers released earlier this year that found cancer patients taking Aranesp had a more probable recurrence of their tumors than those not taking the drug.

Amgen said it notified the Food and Drug Administration but didn’t report the results publicly from the study, which was halted in October of last year, until last month.

Aranesp is Amgen’s best-selling drug with sales topping $4 billion in 2006. It is prescribed to battle anemia associated with chemotherapy and kidney dialysis.

Shares in Amgen were down $2.26, or 3.5 percent, to $62 in afternoon trading Thursday on the Nasdaq Stock Exchange.