Cutaneous extramedullary plasmacytoma: clinical, prognostic, and interphase cytogenetic analysis.

Extramedullary plasmacytoma (EMP) of the skin is a rare indolent neoplasm that shares morphological and immunophenotypic features with plasma cell myeloma (PCM), but the molecular features that distinguish these two entities have not been defined. We reviewed the clinical characteristics, course, and molecular abnormalities in 7 cases of cutaneous EMP (cEMP); 2 patients had primary cEMP and 5 had secondary cEMP. Two patients died of progressive extramedullary plasmacytoma, 1 without PCM; 1 patient who had only a hyperdiploid clone, died within 17 months of the diagnosis of cEMP; and 3 died of PCM. One patient, who had cEMP with a hyperdiploid clone and a 13q deletion, was alive 28 months after diagnosis. Our findings raise questions about the relative prognostic value of molecular aberrations observed in cEMP and PCM. The role of fluorescence in situ hybridization testing in predicting disease progression of cEMP remains to be defined.