Multiparameter flow cytometry (MFC)-based clonality assessment is a powerful method of diagnosis and follow-up in monoclonal gammopathy of undetermined significance (MGUS) and multiple myeloma (MM). However, the relevance of intraclonal heterogeneity in immunophenotypic studies remains poorly understood. The main objective of this work was to characterize the different immunophenotypic subclones in MGUS and MM patients and to investigate their correlation with disease stages. An 8-color MFC protocol with 17 markers was used to identify the subclones within the neoplastic compartment of 56 MGUS subjects, 151 newly diagnosed MM patients, 30 MM subjects in complete remission with detectable minimal residual disease, and 36 relapsed/refractory MM patients. Two or more clusters were observed in > 85% of MGUS subjects, 75% of stage I MM patients, and < 15% in stage III. Likewise, a significant correlation between the dominant subclone size, secondary cytogenetic features, and changes in the expression of CD27, CD44, and CD81 was detected. The loss of intraclonal equilibrium may be an important factor related with kinetics and risk of progression not well considered to date in MFC studies. The MFC strategy used in this work can provide useful biomarkers in MGUS and MM.

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A high variability is observed in the use of rasburicase in our patients. The hematology and pharmacy services have been working jointly to prepare a consensus-based protocol according to which, depending on the patient s risk of developing TLS (tumoral lysis syndrome), standard prophylaxis is administered to low-risk patients (intravenous hydration, alopurinol and urine alcalinization) and rasburicase is administered initially for 1-3 days to patients with high risk of developing TLS.

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Post transplant lymphoproliferative disorders (PTLDs) occur in 0.7-32% of solid organ transplant (SOT) patients.