What is the most likely diagnosis?

C. Peripheral blood and bone marrow reveals the presence of cells characterized by their oval shape, basophilic cytoplasm, eccentric nucleus, and perinuclear cytoplasmic clearing. Some of the cells exhibit higher nuclear-to-cytoplasmic ratios, dispersed chromatin, and prominent nucleoli con sistent with immature plasma cell precursors. Flow cytometry reveals the typical plasma cell markers, CD38 and CD 138, with absence of lymphoid or myeloid markers that would be typical of CLL, ALL, or AML. Lack of CD 56 expression is characteristic to PCL as compared to MM. PCL can present as a primary condition with no antecedent MM, or more commonly evolve from a preceding MM. The diagnosis of PCL is established when the total number of circulating monoclonal plasma cells exceeds 2,000/ jiL or 20% of the total leukocyte count. Thus, in this case, the diagnosis ofPCL is more appropri ate than that of MM. The prognosis of PCL is poor, likely secondary to increased prevalence of high risk cytogenetics. There is no standard treatment regimen, and combinations chemotherapy used for high-risk MM are commonly utilized in addition to hematopoietic stem cell transplantation. Enrol ment into clinical trials is strongly recommended for appropriate patients (Ann Oncol2011;22(7): 1628, Cancer 2009;115(24):5734, Leukemia 2008;22(5):1044).