Methods for treating patients with cancer and autoimmune disorders using IL-28 and IL-29 molecules. The IL-28 and IL-29 molecules include polypeptides that have homology to the human IL-28 or IL-29 polypeptide sequence and proteins fused to a polypeptide with IL-28 and IL-29 functional activity. The molecules can be used as a monotherapy or in combination with other known cancer and/or autoimmune therapeutics.