Minimal residual disease (MRD) assessment is standard in many hematologic malignancies but is considered investigational in multiple myeloma (MM). We report a prospective analysis of the prognostic importance of MRD detection by multiparameter flow cytometry (MFC) in 295 newly diagnosed MM patients uniformly treated in the GEM2000 protocol VBMCP/VBAD induction plus autologous stem cell transplantation [ASCT]). MRD status by MFC was determined at day 100after ASCT. Progression-free survival (PFS; median 71 vs 37 months, P < .001) and overall survival (OS; median not reached vs 89 months, P ‫؍‬ .002) were longer in patients who were MRD negative versus MRD positive at day 100 after ASCT. Similar prognostic differentiation was seen in 147 patients who achieved immunofixation-negative complete response after ASCT. Moreover, MRD ؊ immunofixation-negative (IFx ؊ ) patients and MRD ؊ IFx ؉ patients had significantly longer PFS than MRD ؉ IFx ؊ patients. Multivariate analysis identified MRD status by MFC at day 100 after ASCT as the most important independent prognostic factor for PFS (HR ‫؍‬ 3.64, P ‫؍‬ . IntroductionIn most hematologic malignancies, response to front-line therapy is a good predictor of prognosis, with the longest survival seen in patients achieving an optimal response. This paradigm is represented by chronic myeloid leukemia (CML), in which hematologic, cytogenetic, and molecular remissions define progressively better response to therapy. In consequence, investigations to define these levels of remission are mandatory in routine clinical practice for treatment stratification and assessment of prognosis. 1 The situation is similar for other malignancies such as acute promyelocytic leukemia (APL) or acute lymphoblastic leukemia (ALL). 2,3 For this reason, there are continuous efforts to improve the sensitivity of the methods used to assess response to therapy, mainly through the introduction and refinement of both molecular and immunophenotyping approaches, as well as imaging techniques.Multiple myeloma (MM) should be no exception to this paradigm. For many years, the major goal of MM therapy was to achieve partial response (PR) or disease stabilization. 4,5 With the introduction of high-dose therapy plus autologous stem cell transplantation (HDT/ASCT), the new goal became the achievement of complete response (CR), defined as absence of M-protein by immunofixation (IFx) and less than 5% plasma cells (PCs) in bone marrow (BM). 6,7 More recently, the International Myeloma Working Group proposed a new response category of "stringent CR," which requires normalization of the free light chain ratio and the absence of residual clonal cells in the BM by immunohistochemistry or immunofluorescence. 8 As noted previously, the assessment of minimal residual disease (MRD), residual tumor cells persisting after therapy, is part of the standard of care in many hematologic malignancies, whereas in MM this is still considered investigational. Thus, MRD studies in MM have involved mainly small series of patients or have...

To the best of our knowledge, this is the first prospective analysis in which the prognostic impact of a relatively high number of antigenic markers has been simultaneously analyzed in a large series of uniformly treated patients, showing that the expression of several antigens (particularly CD28 and CD117) on bone marrow plasma cells from patients with MM can help to identify patients at high risk of progression.

Myelomatous plasma cells show a high heterogeneity both in their immunophenotypic characteristics as well as in their cytogenetic features. Thus far, no extensive studies have been carried out to explore whether such antigenic diversity is associated with specific genetic characteristics.We have investigated the relationship between the immunophenotypic profile at plasma cell and both their DNA ploidy status (evaluated by flow cytometry) and specific genetic features (ascertained by fluorescence in situ hybridization) in a large series of 915 patients with newly diagnosed multiple myeloma. The non-hyperdiploid multiple myeloma group (n = 454, 52%) was associated with a significantly higher frequency of positivity for CD28 and CD20 as well as a higher incidence of CD56 À and CD117À cases (P < 0.001). Remarkably, 13q deletion and immunoglobulin heavy chain (IGH) gene rearrangements, which were significantly more common in non-hyperdiploid multiple myeloma, showed a strong association with CD117 À cases. IGH translocation to 11q13 was associated with reactivity for CD20 (P < 0.001), downregulation of CD56 (P < 0.001), and lack of expression of CD117 (P = 0.001). By contrast, IGH translocations to other chromosome partners were almost exclusively found among CD20 À and CD117 À cases (P < 0.001). These results suggest that genetic categories in multiple myeloma exhibit particular immunophenotypic profiles which in turn are strongly associated with the DNA ploidy status.

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