Contributions
Abstract: PB2323
Type: Publication Only
Background
IgM-Monoclonal Gammopathy of Undetermined Significance (MGUS) accounts for 15 to 20% of all MGUS cases and it poses a unique diagnostic challenge as it can be associated with a broad spectrum of pathological processes including both B-cell lymphoproliferative disorders (LPD), and monoclonal-IgM related-disorders (IgM-RD). Among all, IgM-MGUS mostly progresses into Waldenström’s macroglobulinemia (WM). According to the II International Workshop on WM (IWWM), IgM-MGUS and WM can be differentiated by absence versus presence of marrow infiltration by malignant B-cells, while smoldering WM (sWM) from sympomatic WM are differentiated by presence versus absence of clinical findings due to bone marrow (BM) infiltration.
Aims
Based on previous literature data, we aimed to evaluate the contribute of multiparameter flow cytometry (MFC) to discriminate between IgM-MGUS and WM by searching for clonal B-lymphocytes in BM and PB samples.
Methods
A total of 102 patients (64/38, M/F) with a median age of 70 yrs (36-89) were investigated. They were selected among patients with an IgM monoclonal gammopathy not associated with B-cell LPD other than WM. Median serum monoclonal (M)-protein level was 1.0 g/dl (0.2 - 3.9) and light-chain was kappa in 75% of cases. According to the II IWWM criteria, 52 patients were diagnosed as having MGUS, 23 sWM, and 27 WM. Fifty-one BM aspirates and 85 PB samples were immunophenotyped for evaluation of lymphocyte subsets and detection of clonal restriction by Ig Κ and λ light chain analyses on B-cell surface, irrespectively from B-cell proportion; all PB samples resulted positive for clonal restriction, and all BM aspirates were further analyzed with a large panel of MoAbs; data acquisition was performed on a Beckman Coulter Navios flow cytometer and analyses were performed by using Kaluza software.
Results
The median percentage of mature B-cells was found 1.8 (0-50) in PB, and 16 (1.3-50) in BM samples. Overall, in 56 out of 104 patients, clonal B-cells were detected; in particular, clonal restriction was demonstrated in 79% of BM and 40% of PB samples. The FCM results are summarized in the following table with regard to the different diagnosis. Of note, the identification of clonal populations required accurate gating strategies in 5 PB and 1 BM samples because of the presence of low clonal B-cell number within total B-lymphocytes.
| MGUS | sWM | WM | ||||
| PB | BM | PB | BM | PB | BM | |
| Number | 47 | 12 | 16 | 15 | 32 | 24 |
| Median lymphocytes % (range) | 25 (12-38) | 24 (8-41) | 28 (7-51) | 21 (12-34) | 29 (10-65) | 39 (13-61) |
| Median B-lymphocytes % (range) | 3 (0-14) | 3 (1-16) | 1.5 (0-25) | 4 (1-7) | 1.4 (0-50) | 26 (4-50) |
| Cases with clonal restriction (%) | 9 (19) | 5 (42) | 10 (62) | 12 (80) | 15 (68) | 24 (100) |
| Cases with involved/uninvolved light chain >10 | 3 (6) | 4 (33) | 3 (19) | 5 (33) | 7 (32) | 21 (87) |
Conclusion
Our results suggest a pivotal role of MFC in the diagnostic work-up of patients with IgM monoclonal gammopathies. Despite in most cases malignant cells display a non-specific phenotype, accurate gating strategies can enable to identify low-sized clonal populations within normal B-cell background in BM as well as in PB samples. In addition, further studies could establish a possible role of PB FCM studies in the management of patients with IgM monoclonal gammopathies.
Session topic: 19. Non-Hodgkin lymphoma Biology & Translational Research
Abstract: PB2323
Type: Publication Only
Background
IgM-Monoclonal Gammopathy of Undetermined Significance (MGUS) accounts for 15 to 20% of all MGUS cases and it poses a unique diagnostic challenge as it can be associated with a broad spectrum of pathological processes including both B-cell lymphoproliferative disorders (LPD), and monoclonal-IgM related-disorders (IgM-RD). Among all, IgM-MGUS mostly progresses into Waldenström’s macroglobulinemia (WM). According to the II International Workshop on WM (IWWM), IgM-MGUS and WM can be differentiated by absence versus presence of marrow infiltration by malignant B-cells, while smoldering WM (sWM) from sympomatic WM are differentiated by presence versus absence of clinical findings due to bone marrow (BM) infiltration.
Aims
Based on previous literature data, we aimed to evaluate the contribute of multiparameter flow cytometry (MFC) to discriminate between IgM-MGUS and WM by searching for clonal B-lymphocytes in BM and PB samples.
Methods
A total of 102 patients (64/38, M/F) with a median age of 70 yrs (36-89) were investigated. They were selected among patients with an IgM monoclonal gammopathy not associated with B-cell LPD other than WM. Median serum monoclonal (M)-protein level was 1.0 g/dl (0.2 - 3.9) and light-chain was kappa in 75% of cases. According to the II IWWM criteria, 52 patients were diagnosed as having MGUS, 23 sWM, and 27 WM. Fifty-one BM aspirates and 85 PB samples were immunophenotyped for evaluation of lymphocyte subsets and detection of clonal restriction by Ig Κ and λ light chain analyses on B-cell surface, irrespectively from B-cell proportion; all PB samples resulted positive for clonal restriction, and all BM aspirates were further analyzed with a large panel of MoAbs; data acquisition was performed on a Beckman Coulter Navios flow cytometer and analyses were performed by using Kaluza software.
Results
The median percentage of mature B-cells was found 1.8 (0-50) in PB, and 16 (1.3-50) in BM samples. Overall, in 56 out of 104 patients, clonal B-cells were detected; in particular, clonal restriction was demonstrated in 79% of BM and 40% of PB samples. The FCM results are summarized in the following table with regard to the different diagnosis. Of note, the identification of clonal populations required accurate gating strategies in 5 PB and 1 BM samples because of the presence of low clonal B-cell number within total B-lymphocytes.
| MGUS | sWM | WM | ||||
| PB | BM | PB | BM | PB | BM | |
| Number | 47 | 12 | 16 | 15 | 32 | 24 |
| Median lymphocytes % (range) | 25 (12-38) | 24 (8-41) | 28 (7-51) | 21 (12-34) | 29 (10-65) | 39 (13-61) |
| Median B-lymphocytes % (range) | 3 (0-14) | 3 (1-16) | 1.5 (0-25) | 4 (1-7) | 1.4 (0-50) | 26 (4-50) |
| Cases with clonal restriction (%) | 9 (19) | 5 (42) | 10 (62) | 12 (80) | 15 (68) | 24 (100) |
| Cases with involved/uninvolved light chain >10 | 3 (6) | 4 (33) | 3 (19) | 5 (33) | 7 (32) | 21 (87) |
Conclusion
Our results suggest a pivotal role of MFC in the diagnostic work-up of patients with IgM monoclonal gammopathies. Despite in most cases malignant cells display a non-specific phenotype, accurate gating strategies can enable to identify low-sized clonal populations within normal B-cell background in BM as well as in PB samples. In addition, further studies could establish a possible role of PB FCM studies in the management of patients with IgM monoclonal gammopathies.
Session topic: 19. Non-Hodgkin lymphoma Biology & Translational Research