P04 multiparametric flow cytometry refines risk stratification in newly diagnosed multiple myeloma patients

The European Myeloma Network has underlined the clinical utility of multiparametric flow-cytometry (MFC) analysis in the work-up and follow-up of multiple myeloma (MM) patients. The prerequisite of MFC in MM is to discriminate within the whole PC compartment between normal and aberrant clonal PCs. Clonal PCs show a heterogeneous expression of CD19, CD45lo and CD56−/lo, together with high amounts of CD38, CD138 and cVS38. Their identification is favored by the concomitant expression of other surface antigens, such as CD28, CD20, CD33, CD13, CD117, CD56. The definition of clonal PCs is established due to the variable association of these antigens together with cytoplasmic immunoglobulin k or λ chain staining. Between 2018 and 2022, we prospectively analyzed by flow cytometry BM samples from 84 consecutive newly diagnosed MM patients managed at the Hematology Center of the Sapienza University of Rome to assess the immunophenotypic characteristics of clonal PCs and to investigate the possible correlation between the aberrant phenotype, the clinical characteristics of the disease and cytogenetic abnormalities Fifty-two pts were males and the median age was 61 years (28-88). Thirty-eight % of patients were ISS I and 46% were R-ISS II. Fifteen % of patients showed high-risk cytogenetic abnormalities. Eighty-five % of patients were considered eligible for ASCT. The main therapeutic regimens used were bortezomib-based combinations, such as VTd in transplant eligible patients and VMP in transplant ineligible patients. The baseline clinical characteristics and the frontline induction treatments are summarized in Table 1a and 1b, respectively. BM clonal PCs from a minority of patients of our cohort presented early B-cell maturation antigen expression, such as CD19 (2%), while CD20 and CD45 were detected in 17% and 52% of the clonal PCs, respectively. In 69% of cases, BM PCs showed a bright CD56 surface expression. Among the remaining patients, 1% showed a reduced reactivity for CD56 while CD56 was completely negative in the other cases (30%). CD117 was detected in 42% of clonal BM PCs, while CD28 and CD33 were detected in 15% and 5% of clonal PCs, respectively. When considering unusual antigens on the surface of aberrant PCs (CD28, CD20 and CD45) we observed that the expression of CD28 was mutually exclusive compared to CD56 (p<0.001). The presence of CD20 was associated with the absence of CD28 (p=0.048). Expression of CD28 on clonal PCs was associated with a significantly lower median number of platelets at baseline (p=0.005) and with a significantly reduced percentage of MM patients achieving a complete response (p=0.038). Focusing on high-risk chromosomal aberrations, t(14;16) tended to associate with CD28 expression (p=0.079), while t(4;14) tended to associate with a lower median value of CD138 mean fluorescence intensity (MFI) (p=0.06). We also observed that CD20 expression on clonal PCs (18% of all patients) was associated with the type of secretory MM (p=0.041). Patients with CD2O expression showed a higher median level of serum monoclonal protein at baseline compared to patients lacking CD20 (p=0.038). Despite the relatively limited sample size, these data confirm that the antigenic surface profile of MM PCs is highly variable, in line with the characteristic heterogeneity of the disease. MFC represents a simple, reproducible, and cost-effective tool which could help to identify MM subsets at diagnosis and improve risk stratification. Table 1a - Patient’s baseline characteristics N=84 (%) Median age, years (range) <65/≥65 61.3 (27.9 – 88.2)54/30 Gender Male, n(%) Female, n(%) 52 (62)32 (38) Type of MM ClassicMicromolecularNon secreting 76 (91)6 (7)2 (2) Type of heavy chain GNon GNo monoclonal component 51 (61)32 (38)1 (1) Type of light chain kλk + λNA* 60 (69)22 (26)2 (2)2 (2) CRAB Ca++ ≥12 mg/dlCr >2 mg/dlHb <10 g/dlOsteolytic bone lesions 5 (6)7 (8)27 (32)69 (82) Bone marrow plasma cells infiltration, median % (range) 30 (10-90) ISS, n (%) IIIIIINA 32 (38)20 (24)26 (31)8 (9) High-risk FISH cytogenetics, n (%) NoYesNA 67 (85)12 (15)5 (6) High-risk FISH cytogenetics ± ampl/gain1q, n (%) NoYesNA 45 (57)34 (43)5 (6) R-ISS, n (%) IIIIIINA 22 (26)39 (46)16 (19)13 (15) ASCT eligible Yes, n (%) No, n(%) 71 (85)13 (15) Overall response rate (ORR) 70 (85) *NA: not available Table 1b - Patient’s baseline induction therapy Transplant eligible patients N=71 (84%) Induction therapy VTdD-VRdVRr 59 (90)3 (5)3 (5) ASCT SingleTandemNo ASCT* 37 (52)11 (15)23 (32) Maintenance LenalidomideLenalidomide plus anti-CD38No therapy** 43 (61)3 (4)25 (35) Toxicity Hematological -Anemia-Thrombocytopenia Non-hematological -Neuropathy-Infections-Thromboembolic events-Allergic reactions-Others 3 (4)1 (1)2 (3)21 (46)10 (15)3 (4)2 (3)1 (1)4 (6) Transplant ineligible patients N=13 (16%) Induction therapy VMPRdKdVRd 7 (54)2 (15)2 (15)1 (8) Toxicity Hematological -Anemia Non-hematological -Infections 2 (15)2 (15)2 (15)2 (15) *No ASCT: 9 pts waiting for ASCT**No therapy: waiting to start maintenance therapy