Background: Cutaneous plasmacytoma is a well-recognized, yet infrequent, occurrence in multiple myeloma (MM). There are limitations in the morphologic assessment, and as such, the diagnosis presents some difficulty, particularly with the plasmablastic type.

Methods: Pathology reports of 2357 patients with a diagnosis of MM were reviewed. Twenty patients yielded a total of 25 plasmacytomas, 10 of which were analyzed for syndecan-1 immunoreactivity. Bartl grade of bone marrow and cutaneous plasmacytoma was compared and immunoglobulin secretory status of the patients was assessed.

Results: The incidence of cutaneous plasmacytoma was found to be 1 in 118 patients with MM. Immunoglobulin secretion was found to be predominantly IgG. There was a trend for the plasmacytoma Bartl grade to be equal to or greater than that of the corresponding bone marrow Bartl grade, suggesting a more aggressive phenotype in the metastatic lesion.

Conclusions: Syndecan-1 was found to be a sensitive marker for plasmacytomas, independent of cytologic differentiation.