NEW YORK (AP) ¿ Genentech Inc. and partner Biogen Idec Inc. said Wednesday the Food and Drug Administration is withholding a decision to expand approval of Rituxan as a leukemia treatment, pending further discussion. Neither company disclosed the specific nature of the FDA's "complete response letter," which is typically a request for some type of information or input. The companies did say the FDA is not asking for new data on the drug and that it is still in discussion over the drug's labeling. Genentech would not comment further on the letter or discussions around the label, which lists the drug's intended use and any side effects. The drug is already approved as a treatment for rheumatoid arthritis and non-hodgkin's lymphoma, a type of cancer. Biogen and Genentech, which is now part of Swiss drug developer Roche, sell the drug through a partnership. The FDA did not ask for new data on the current application, which seeks approval as a treatment for chronic lymphocytic leukemia. It is the most common adult leukemia in the U.S. Genentech and Biogen said they will continue final label discussions with the FDA. Shares of Biogen, which is based in Cambridge, Mass., closed up 11 cents at $46.16 during the regular trading session.