The immunohistochemical detection of syndecan-1 (belonging to the cluster CD138) is a sensitive and reliable method for identifying normal and neoplastic plasma cells. It may be used in para-ffinmbedded bone marrow specimens, as well as in extramedullary tumours of unknown origin. The three anaplastic tumours reported by us in the lymph node, the gingiva, and pleura were negative for other markers, but the syndecan-1 positivity elucidated their plasmocytic histogenesis.

        Key words: plasma cells - anaplastic myeloma - syndecan-1 (CD138) - immunohistochemistry