We provide an antibody capable of binding to an intracellular PRL-I or PRL-3 polypeptide, in which the antibody is capable of binding to an epitope bound by antibody 269, antibody 223 or antibody 318. Such anti-PRL antibodies may be capable of binding to intracellular PRL-I or PRL-3. They may be suitable for use as therapies against cancer or metastasis thereof, or in clinical diagnosis to identify PRL-3 or PRL-1 positive patients.