on behalf of the GEM (Grupo Españ ol de Mieloma)/PETHEMA (Programa para el Estudio de la Terapé utica en Hemopatías Malignas) cooperative study groupsThe presence of CD19 in myelomatous plasma cells (MM-PCs) correlates with adverse prognosis in multiple myeloma (MM). Although CD19 expression is upregulated by CD81, this marker has been poorly investigated and its prognostic value in MM remains unknown. We have analyzed CD81 expression by multiparameter flow cytometry in MM-PCs from 230 MM patients at diagnosis included in the Grupo Españ ol de Mieloma (GEM)05465years trial as well as 56 high-risk smoldering MM (SMM). CD81 expression was detected in 45% (103/230) MM patients, and the detection of CD81 þ MM-PC was an independent prognostic factor for progression-free (hazard ratio ¼ 1.9; P ¼ 0.003) and overall survival (hazard ratio ¼ 2.0; P ¼ 0.02); this adverse impact was validated in an additional series of 325 transplant-candidate MM patients included in the GEM05 o65 years trial. Moreover, CD81þ SMM (n ¼ 34/56, 57%) patients had a shorter time to progression to MM (P ¼ 0.02). Overall, our results show that CD81 may have a relevant role in MM pathogenesis and represent a novel adverse prognostic marker in myeloma.

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