This document relates to the activity of interferon regulatory factor 4 (IRF4) in T-cell lymphomas. For example, methods and materials involved in reducing the expression of an IRF4 polypeptide in T-cell lymphoma cells and identifying agents having the ability to reduce expression of an IRF4 polypeptide in T-cell lymphoma cells are provided. This document also relates to reducing DUSP22 or FLJ43663 polypeptide activity in T-cell lymphomas. For example, methods and materials involved in reducing the expression of DUSP22 polypeptides and/or FLJ43663 polypeptides in T-cell lymphoma cells and identifying agents having the ability to reduce expression of DUSP22 polypeptides and/or FLJ43663 polypeptides in T-cell lymphoma cells are provided.