Most flow cytometry panels for plasma cells include CD19, CD20, CD38, CD45, CD56, CD138, and cytoplasmic kappa and lambda light chains.
Normal plasma cells are CD19+, CD38-, CD45+, CD56-, CD138+, and CD48dim.
In contrast, myeloma plasma cells show loss of CD19 and aberrant expression of CD56 and CD117 (CD19-, CD56+, CD117+). Light chain clonality can be assessed after plasma cells are permeabilized, due to the cytoplasmic localization of immunoglobulins.


Report of the European Myeloma Network on multiparametric flow cytometry in multiple myeloma and related disorders.
Haematologica. 2008 Mar;93(3):431-8.
Rawstron AC, Orfao A, Beksac M, Bezdickova L, Brooimans RA, Bumbea H, Dalva K, Fuhler G, Gratama J, Hose D, Kovarova L, Lioznov M, Mateo G, Morilla R, Mylin AK, Omedé P, Pellat-Deceunynck C, Perez Andres M, Petrucci M, Ruggeri M, Rymkiewicz G, Schmitz A, Schreder M, Seynaeve C, Spacek M, de Tute RM, Van Valckenborgh E, Weston-Bell N, Owen RG, San Miguel JF, Sonneveld P, Johnsen HE; European Myeloma Network.
This report indicates several technical recommendations for the correct identification of malignant plasma cells by flow cytometry. Recommendations included:
  1 - The primary gating strategy should be based on CD38 vs CD138 expression, to ensure that CD45+ plasma cells are not excluded
  2 - Plasma cells should be identified and counted by simultaneous expression of CD38, CD138 and CD45
  3 - The panel for abnormal plasma cells should include at least CD19 and CD56 (essential), and also CD20, CD27, CD28, and CD117 (recommended)

Review of phenotypic markers used in flow cytometric analysis of MGUS and MM, and applicability of flow cytometry in other plasma cell disorders.
Br J Haematol. 2010 May;149(3):334-51.
Raja KR, Kovarova L, Hajek R.


Clinical applications of flow cytometry in multiple myeloma:


1 - Minimal residual disease: assessing response to therapy

Current therapeutic approach to MM has evolved to the point that complete responses have become a realistic goal after stem cell transplantation (SCT). The traditional methods to assess response to treatment in MM are the tumor markers (serum and urine paraproteins), and the percentage of plasma cells in the bone marrow. Flow cytometry not only can be used as a quick and efficient technique of confirming the presence of a complete response, but it provides a more sensitive method to assess complete response, because it offers a sensitivity of 0.01%.

Flow cytometry is currently considered to be the method of choice for assessing minimal residual disease in MM.

Circulating plasma cells in multiple myeloma: characterization and correlation with disease stage.
Br J Haematol. 1997 Apr;97(1):46-55.
Rawstron AC, Owen RG, Davies FE, Johnson RJ, Jones RA, Richards SJ, Evans PA, Child JA, Smith GM, Jack AS, Morgan GJ.
Circulating plasma cells were detected by flow cytometry in the peripheral blood of:
  - 38 of 51 (75%) patients with multiple myeloma at diagnosis
  - 11 of 12 (92%) patients at disease relapse
  - 4 of 10 (40%) apheresis products from stem cell collection
  - 0 of 9 patients in CR
  - 0 of 10 normal donors
Sensitivity of flow cytometry  was up to 1:10,000 cells.

A single-tube six-colour flow cytometry screening assay for the detection of minimal residual disease in myeloma.
Leukemia. 2007 Sep;21(9):2046-9.
de Tute RM, Jack AS, Child JA, Morgan GJ, Owen RG, Rawstron AC.

Flow cytometric minimal residual disease monitoring in patients with multiple myeloma undergoing autologous stem cell transplantation: a retrospective study.
Leuk Lymphoma. 2008 Feb;49(2):306-14.
Liu H, Yuan C, Heinerich J, Braylan R, Chang M, Wingard J, Moreb J.
Flow cytometry of the bone marrow before and after autologous stem cell transplant was obtained in 39 patients with multiple myeloma. Normal plasma cells were distinguished from aberrant plasma cells based on the expression of CD38, CD45, CD56, and CD19. A detectable population of aberrant plasma cells was found in all patients before the transplant, and in 52% of cases after the transplant. Survival analysis showed a correlation between the detection of aberrant plasma cells in the flow cytometry of the bone marrow aspirates after the transplant, and a poorer progression-free survival.

Comparison of immunofixation, serum free light chain, and immunophenotyping for response evaluation and prognostication in multiple myeloma.
J Clin Oncol. 2011 Apr 20;29(12):1627-33.
Paiva B, Martinez-Lopez J, Vidriales MB, Mateos MV, Montalban MA, Fernandez-Redondo E, Alonso L, Oriol A, Teruel AI, de Paz R, Laraña JG, Bengoechea E, Martin A, Mediavilla JD, Palomera L, de Arriba F, Bladé J, Orfao A, Lahuerta JJ, San Miguel JF.
This is a prospective study comparing the prognostic impact of conventional CR (= negative immunofixation + <5% plasma cells in the bone marrow), stringent CR (= CR + normal serum free kappa/lambda ratio), and immunophenotypic remission (= flow cytometry negative) in 102 patients with newly diagnosed multiple myeloma. Discrepancies between the results of the three techniques were common. Patients in stringent CR did not have a survival advantage compared with patients in conventional CR (but follow-up was limited). Instead, patients with negative flow cytometry had a better progression-free survival and overall survival than patients in conventional CR or stringent CR. Interestingly, patients with negative flow cytometry but positive immunofixation had a better prognosis than patients with positive flow cytometry and negative immunofixation. In fact, in patients with negative flow cytometry, the paraprotein disappeared with time, whereas patients with positive flow cytometry and negative immunofixation eventually experienced reappearance of the paraprotein and disease relapse/progression. In conclusion, the achievement of remission by flow cytometry led to longer remissions than the achievement of CR by immunofixation or free light chain ratio.


2 - Minimal residual disease: regular monitoring to detect early relapse

Flow cytometry has an established role in disease monitoring of MM.

Minimal residual disease monitoring in multiple myeloma.
Best Pract Res Clin Haematol. 2002 Mar;15(1):197-222.
Davies FE, Rawstron AC, Owen RG, Morgan GJ.

A study of 45 patients undergoing stem cell transplantation showed detectable plasma cells at 3 months after transplantation in 42% of cases, and these patients had a shorter progression-free survival than those with no detectable disease (20 vs 35 months, respectively):

Flow cytometric disease monitoring in multiple myeloma: the relationship between normal and neoplastic plasma cells predicts outcome after transplantation.
Blood. 2002 Nov 1;100(9):3095-100.
Rawstron AC, Davies FE, DasGupta R, Ashcroft AJ, Patmore R, Drayson MT, Owen RG, Jack AS, Child JA, Morgan GJ.
This study evaluates by flow cytometry both normal and neoplastic plasma cells in the bone marrow of 45 patients after stem cell transplant. Myeloma cells were detectable at 3 months after transplant in 42% of all patients, and in 9 of 33 (27%) of patients with IFE-negative CR . Flow cytometry was more sensitive than IFE for the assessment of CR in the post-transplant period. Flow cytometry had prognostic implications, because patients with positive flow cytometry had a median PFS of 20 months, whereas patients with negative flow cytometry had a median PFS of 35 months (p= 0.003).

Of note, 27% of patients had detectable neoplastic plasma cells even in front of negative immunofixation. These patients would have been presumed to be in complete remission without the results of the flow cytometry. Therefore, conventional monitoring strategies for MM such as serum immunofixation are not sufficiently sensitive to detect a true complete remission (in fact, the sensitivity threshold of serum immunofixation is approximately 100 mg/dL of monoclonal protein).

PCR is another technique able to detect minimal residual disease in MM. However, a study comparing flow cytometry with PCR in the detection of minimal residual disease in MM, has concluded that flow cytometry is the preferred method: although PCR was slightly more sensitive and specific than flow cytometry, it was applicable in a lower proportion of MM patients (50%), and it was more expensive and time-consuming, while flow cytometry provided similar prognostic information, and it is applicable in virtually all patients:

Minimal residual disease monitoring in multiple myeloma: a comparison between allelic-specific oligonucleoide real-time quantitative polymerase chain reaction and flow-cytometry.
Haematologica. 2005 Oct;90(10):1365-72.
Sarasquete ME, García-Sanz R, González D, Martínez J, Mateo G, Martínez P, Ribera JM, Hernández JM, Lahuerta JJ, Orfão A, González M, San Miguel JF.
This study compared quantitative PCR and flow cytometry (FCM) for the detection of minimal residual disease in multiple myeloma. The authors analyzed 32 bone marrow samples of patients in complete remission after stem cell transplant both by PCR and flow cytometry. Because of technical reasons, PCR was feasible in 75% of patients, while flow cytometry was feasible in up to 90% of patients. Therefore, both tests were obtained simultaneously in only 24 patients. PCR was more sensitive than flow cytometry, because it detected residual myeloma cells in 17 patients, whereas floww cytometry detected residual cells in 11 patients. The authors concluded that both PCR and flow cytometry are acceptable methods and provide equivalent prognostic information. PCR was more sensitive, but it was time-consuming and technically feasible in a lower proportion of patients.

Minimal residual disease monitoring in multiple myeloma: flow cytometry is the method of choice.
Br J Haematol. 2005 Mar;128(5):732-3.
Owen RG, Rawstron AC.

Monitoring of minimal residual disease in multiple myeloma after allo-SCT: flow cytometry vs PCR-based techniques.
Bone Marrow Transplant. 2008 May;41(10):913-6.
Lioznov M, Badbaran A, Fehse B, Bacher U, Zander AR, Kröger NM.


3 - Diagnosis of non-secretory myeloma

Flow cytometry analysis of cytoplasmic immunoglobulin content can detect monoclonal plasma cells in patients with non-secretory myeloma, where tumor markers are absent.

The frequency of non-secretory MM is low (approximately 1% of MM), but in these patients, infiltration of clonal plasma cells in the bone marrow found on flow cytometry would confirm a diagnosis of MM, while the diagnosis would be missed by the simple morphologic analysis of the bone marrow in those MM cases with only a mild plasmacytosis (<10% plasma cells).

Cytoplasmic immunoglobulin content in multiple myeloma.
J Clin Invest. 1985 Aug;76(2):765-9.
Barlogie B, Alexanian R, Pershouse M, Smallwood L, Smith L.


4 - Diagnosis of true solitary bone plasmacytoma

When a patient with a single bone lesion has a negative bone marrow biopsy, the diagnosis is “solitary plasmacytoma”, and the treatment of choice is local radiotherapy. However, since flow cytometry can detect minimal amount of plasma cell involvement in the bone marrow, a positive result would change the diagnosis to multiple myeloma with a single bone lesion, a situation for which radiotherapy has no role, and systemic therapy including transplant is usually indicated.

Multiparameter flow cytometry for staging of solitary bone plasmacytoma: new criteria for risk of progression to myeloma.
Blood. 2014 Aug 21;124(8):1300-3.
Paiva B, Chandia M, Vidriales MB, Colado E, Caballero-Velázquez T, Escalante F, Garcia de Coca A, Montes MC, Garcia-Sanz R, Ocio EM, Mateos MV, San Miguel JF.
Flow cytometry for detecting plasma cells was obtained in the marrow aspirates of 35 patients with solitary plasmacytoma of the bone, and 29 patients with extramedullary plasmacytoma. Among patients with solitary plasmacytoma of the bone, 17 (49%) were positive, and 71% of them  progressed to multiple myeloma (vs 8% of flow-negative patients).


5 - Diagnosis of extramedullary plasmacytoma

Development of soft tissue masses in patients with multiple myeloma can be due to progressive disease with extramedullary involvement (which confers a poor prognosis, often <6 months), or other causes, such as amyloidomas, infections, and secondary malignancies. FNA may be required for differential diagnosis. Flow cytometry can confirm the diagnosis of extramedullary myeloma.

Flow cytometry is also useful in the evaluation of malignant effusions of MM.

Soft tissue masses in patients with multiple myeloma: a fine-needle aspiration study of 30 cases with flow cytometry and clinical correlation.
Cancer. 2001 Aug 25;93(4):257-62.
Mukunyadzi P, Bardales RH, Wilson CS, Sawyer JR, Stanley MW.
In this study, 27 myeloma patients underwent fine-needle aspiration of soft tissue masses, and  flow cytometry with cIg provided the diagnosis of myeloma in all cases. The procedure was particularly useful in 3 patients who had a negative bone marrow biopsy.

Cytology and flow cytometry of malignant effusions of multiple myeloma.
Diagn Cytopathol. 2000 Mar;22(3):147-51.
Palmer HE, Wilson CS, Bardales RH.
This study showed that flow cytometry is useful in the evaluation of malignant effusions of MM: a malignant plasma cell population was identified in 9 of 10 pleural or pericardial fluids submitted for flow cytometry, including 2 fluids with negative cytology.

Flow cytometry characterization in central nervous system and pleural effusion multiple myeloma infiltration: an Italian national cancer institute experience.
Br J Haematol. 2016 Mar;172(6):980-2.
Marchesi F, Masi S, Summa V, Gumenyuk S, Merola R, Orlandi G, Cigliana G, Palombi F, Pisani F, Romano A, Spadea A, Papa E, Canfora M, De Bellis F, Conti L, Mengarelli A, Cordone I.


6 - Flow cytometry of peripheral blood: diagnosis of plasma cell leukemia

The usefulness of this application is self-evident, as morphology of circulating neoplastic plasma cells does not always reflect the mature Marschalko-type appearance of normal plasma cells.


7 - Flow cytometry of peripheral blood: quantify level of circulating tumor cells

Levels of circulating plasma cells in the peripheral blood are a known prognostic factor in MM patients. In a study, the prognostic value of circulating plasma cells detected by flow cytometry of the peripheral blood was independent of beta2-microglobulin and albumin, the two parameters currently used in the new ISS staging system:

Circulating plasma cells detected by flow cytometry as a predictor of survival in 302 patients with newly diagnosed multiple myeloma.
Blood. 2005 Oct 1;106(7):2276-9.
Nowakowski GS, Witzig TE, Dingli D, Tracz MJ, Gertz MA, Lacy MQ, Lust JA, Dispenzieri A, Greipp PR, Kyle RA, Rajkumar SV.
This study evaluated prognosis according to the number of circulating plasma cells tested by flow cytometry of peripheral blood in 302 myeloma patients.
Circulating plasma cells per 50,000 mononuclear cells were:
  - 0 circulating plasma cells in 80 (27%) patients
  - 1-10 circulating plasma cells in 106 (35%) patients
  - >10 circulating plasma cells in 115 (38%) patients
Median overall survival was:
  - 47 months for the whole group
  - 59 months for patients with 10 or fewer circulating plasma cells
  - 37 months for patients with >10 circulating PCs
Multivariate analysis showed that the number of circulating plasma cells was an independent predictor of survival. Its prognostic value was independent of other known prognostic factors, such as albumin and b2m.

Flow cytometric detection of circulating myeloma cells before transplantation in patients with multiple myeloma: a simple risk stratification system.
Blood. 2006 Apr 15;107(8):3384-8.
Dingli D, Nowakowski GS, Dispenzieri A, Lacy MQ, Hayman SR, Rajkumar SV, Greipp PR, Litzow MR, Gastineau DA, Witzig TE, Gertz MA.
This study evaluated circulating myeloma cells in 246 patients undergoing autologous stem cell transplantation. Circulating tumor cells were detected by flow cytometry at the time of stem cell collection. 95 patients were found to have circulating cells. No difference in CR rate was found between the group with circulating cells (32%) and the group without circulating cells (36%), but the group with circulating cells had a shorter time to progression (14 vs 22 months, p= 0.001) and a shorter overall survival (33 vs 59 months, p= 0.01). The presence of circulating tumor cells was a prognostic factor independent of cytogenetics and disease status at the time of transplant.


8 - Quantification of contamination by tumor cells in harvested stem cells

The usefulness of this application is self-evident, especially in patients with a previous diagnosis of circulating plasma cells or plasma cell leukemia.


9 - Differential diagnosis of MM vs MGUS vs reactive plasmacytosis

A small percentage of MM patients have no complications from the disease (no anemia, no hypercalcemia, no renal insufficiency, no bone lesions, etc.). In these patient, the differential diagnosis includes MGUS vs MM in stage IA (according to the Durie-Salmon stage). Although the distinction between plasma cell involvement of bone marrow in MGUS and MM is arbitrary (<10% in MGUS and >10% in MM), this threshold confers practical implications for diagnosis and treatment. Flow cytometry is particularly useful in those patients with low tumor burden, because it defines with precision the percentage of clonal plasma cells infiltrating the bone marrow. Moreover, in patients without paraproteins, flow cytometry can distinguish whether the plasma cells in the bone marrow can be polyclonal (= reactive plasmacytosis) instead of monoclonal (= MM or MGUS).


10 - Differentiation between myeloma and lymphoma

The histologic appearance of myeloma can be confused with that of lymphoplasmacytic lymphoma (LPL)/ Waldenstrom macroglobulinemia and marginal zone lymphoma (MZL), two types of non-Hodgkin lymphoma with plasmacytic differentiation. Flow cytometry can help in the differential diagnosis:
  - Myeloma = CD19-, CD56+, CD45dim/-
  - MZL = CD19+, CD56-, CD45+
  - LPL = CD19+, CD138- (but it can be +)

Immunophenotypic differentiation between neoplastic plasma cells in mature B-cell lymphoma vs plasma cell myeloma.
Am J Clin Pathol. 2007 Feb;127(2):176-81.
Seegmiller AC, Xu Y, McKenna RW, Karandikar NJ.

Based on morphologic features, it may be difficult to differentiate between plasmacytomas and non-Hodgkin lymphomas with plasmacytic differentiation. This study shows that immunophenotyping by flow cytometry can differentiate between these two pathologic entities: plasma cells in non-Hodgkin lymphoma are usually CD19+, CD45+, CD56-, and sIg+, while plasmacytomas usually have the reverse phenotype. CD19 and CD56 are the most useful markers for the differential diagnosis (plasma cells in solitary plasmacytoma of bone and multiple myeloma are usually CD19- and CD56+). Based on immunophenotyping, some cases of extramedullary plasmacytomas can be reclassified as MZL or other B-cell NHL with plasmacytic differentiation.


11 - Possible implications for therapy with monoclonal antibodies

Rituximab (Rituxan®), alentuzumab (Campath®), and gentuzumab (Mylotarg®) are monoclonal antibodies directed against CD20, CD52, and CD33 antigens, respectively. Although currently FDA guidelines do not approve the use of these three monoclonal antibodies in MM, one could make the case for their off-label use in specific patients, especially when all other conventional therapies have been exhausted and the disease is refractory to any other therapeutic approach.

A series of flow cytometric immunophenotyping in 306 patients with MM has shown that approximately 10% of MM patients have neoplastic plasma cells expressing CD20, and 5% expressing CD52:

Flow cytometric immunophenotypic analysis of 306 cases of multiple myeloma.
Am J Clin Pathol. 2004 Apr;121(4):482-8.
Lin P, Owens R, Tricot G, Wilson CS.
Flow cytometry was obtained in the bone marrow aspirates of 306 myeloma patients. Antigen expression was moderate-bright as follows:
  - CD56: 72%
  - CD117: 18%
  - CD20: 9% (target of rituximab)
  - CD45: 9%
  - CD52: 5% (target of alentuzumab)
  - CD19: <1%

CD33 is expressed on plasma cells of a significant number of myeloma patients, and may represent a therapeutic target.
Leukemia. 2005 Nov;19(11):2021-2.
Robillard N, Wuillème S, Lodé L, Magrangeas F, Minvielle S, Avet-Loiseau H.
This study of 63 patients with MM detected the expression of CD33 in 35% of cases. When detected, the expression was found in 11-100% of the myeloma cells.


12 - Prognosis

See specific section.

New criteria to identify risk of progression in monoclonal gammopathy of uncertain significance and smoldering multiple myeloma based on multiparameter flow cytometry analysis of bone marrow plasma cells.
Blood. 2007 Oct 1;110(7):2586-92.
Pérez-Persona E, Vidriales MB, Mateo G, García-Sanz R, Mateos MV, de Coca AG, Galende J, Martín-Nuñez G, Alonso JM, de Las Heras N, Hernández JM, Martín A, López-Berges C, Orfao A, San Miguel JF.
This is a study of 407 patients with MGUS and 93 patients with smoldering myeloma. Normal and myelomatous plasma cells were differentiated by flow cytometry, based on the expression of 4 antigens (CD19, CD45, CD38, and and CD56). The authors showed that patients with predominance of aberrant plasma cells at diagnosis had a significantly higher risk of progressing to multiple myeloma. After multivariate analysis, the percentage of aberrant plasma cells in the bone marrow retained its prognostic significance.

Lack of CD56 expression on myeloma cells is not a marker for poor prognosis in patients treated by high-dose chemotherapy and is associated with translocation t(11;14).
Bone Marrow Transplant. 2007 Dec;40(11):1033-7.
Hundemer M, Klein U, Hose D, Raab MS, Cremer FW, Jauch A, Benner A, Heiss C, Moos M, Ho AD, Goldschmidt H.
Lack of CD56 expression in myeloma cells was believed to be associated with poor prognosis. This study in cells of 99 evaluated by flow cytometry the CD56 expression in cells of 99 patients prior to transplant. No statistically significant difference was found between the EFS of 28 patients with CD56- MM and the EFS of 71 patients with CD56+ MM. The lack of CD56 expression on malignant plasma cells correlated with the presence of the t(11;14) translocation.

Quantification of clonal circulating plasma cells in relapsed multiple myeloma.
Br J Haematol. 2014 Nov;167(4):500-5.
Gonsalves WI, Morice WG, Rajkumar V, Gupta V, Timm MM, Dispenzieri A, Buadi FK, Lacy MQ, Singh PP, Kapoor P, Gertz MA, Kumar SK.
Circulating plasma cells were quantified by multi-parameter flow cytometry in 647 patients with relapsed multiple myeloma. Circulating plasma cells were absent in patients in coimplete remission, whereas the presence of 100 or more circulating plasma cells (per 150,000 gated mononuclear events) was associated with an inferior median survival (12 months vs 33 months). The adverse impact on prognosis was maintained at multivariate analysis.

Minimal residual disease in myeloma by flow cytometry: independent prediction of survival benefit per log reduction.
Blood. 2015 Mar 19;125(12):1932-5.
Rawstron AC, Gregory WM, de Tute RM, Davies FE, Bell SE, Drayson MT, Cook G, Jackson GH, Morgan GJ, Child JA, Owen RG.
The authors assessed the presence of minimal residual disease (MDR) by flow cytometry in 397 patients with multiple myeloma, treated in the Medical Research Council Myeloma IX study (this included autologous stem cell transplant). They found that median overall survival increased for each log depletion in the MDR level:
  -     >10%  : 1    year
  -    1-10%  : 4    years
  -  0.1-1%   : 5.9  years
  - 0.01-0.1% : 6.8  years
  -     <0.01%: >7.5 years

Depth of Response in Multiple Myeloma: A Pooled Analysis of Three PETHEMA/GEM Clinical Trials.
J Clin Oncol. 2017 Sep 1;35(25):2900-2910.
Lahuerta JJ, Paiva B, Vidriales MB, Cordón L, Cedena MT, Puig N, Martinez-Lopez J, Rosiñol L, Gutierrez NC, Martín-Ramos ML, Oriol A, Teruel AI, Echeveste MA, de Paz R, de Arriba F, Hernandez MT, Palomera L, Martinez R, Martin A, Alegre A, De la Rubia J, Orfao A, Mateos MV, Blade J, San-Miguel JF; GEM (Grupo Español de Mieloma)/PETHEMA (Programa para el Estudio de la Terapéutica en Hemopatías Malignas) Cooperative Study Group.
These authors analyzed data of flow cytometry to assess minimal residual disease (MRD) in 609 patients enrolled in previous clinical trials. They found that the achievement of a stringent complete remission by flow cytometry was associated with a superior long-term survival. The achievement of MRD-negative status had a better prognostic value than the achievement of CR (complete remission, traditionally defined as a negative immunofixation and <5% plasma cells in the bone marrow). The authors conclude that MRD negativity should one of the most important end point for the treatment of multiple myeloma in eligible patients (i.e., those who can undergo a stem cell transplant or those without major comorbidities that prevent the administration of adequate chemotherapy regimens).



CD20 is associated with a small mature plasma cell morphology and t(11;14) in multiple myeloma.
Blood. 2003 Aug 1;102(3):1070-1.
Robillard N, Avet-Loiseau H, Garand R, Moreau P, Pineau D, Rapp MJ, Harousseau JL, Bataille R.
Results of the study:
  - CD20 was found to be expressed in 12 of 66 (18%) myeloma patients.
  - In 5 of 50 (10%) patients, CD20+ cells represented 100% of myeloma cells at the time of diagnosis.
  - A small mature plasma cell morphology was found in 58% of patients with CD20+ plasma cells and 7% of patients with CD20 negative plasma cells.
  - 80% of patients with 100% CD20+ plasma cells had a small mature plasma cell morphology.
  - The translocation t(11;14) was more frequently found in patients with CD20+ plasma cells than in those with CD20 negative plasma cells (83% vs 9%, p <0.001).
  - All patients with 100% CD20+ plasma cells had the translocation t(11;14)
  - 66% of patients with t(11;14) had CD20+ plasma cells
  - Only 4% of patients without the translocation t(11;14) had CD20+ plasma cells
 In conclusion, CD20 expression was associated with small mature plasma cell morphology and t(11;14).

Instability of immunophenotype in plasma cell myeloma.
Am J Clin Pathol. 2008 Jun;129(6):926-33.
Cao W, Goolsby CL, Nelson BP, Singhal S, Mehta J, Peterson LC.
In this study of flow cytometry in 56 myeloma patients, 23 patients (41%) showed a change in immunophenotype (CD52 in 17 cases,  CD20 in 7 cases, and CD56 in 6 cases). The instability of the immunophenotype in multiple myeloma can have important implications, especially in the detection of residual disease, and when considering the potential application of antigen-directed therapy.



Giampaolo Talamo, M.D.