Celgene thinks ozanimod -- which it picked up with the Receptos acquisition last year -- could reach peak annual sales of $4 billion to $6 billion. That estimated range includes the drug's other targeted indication, multiple sclerosis. The ulcerative colitis market could be big for Celgene, though, since ozanimod is taken orally instead of by injection or infusion, like current leading drugs Humira and Remicade.