Correspondence
in the article, several (undefined) criteria are merged under
the term BM findings.
On the basis of all the above, we sincerely believe that
the recommendations made by Pozdnyakova et al1 about
the potential utility of the newly proposed phenotypic
criterion are not supported by our findings, as well as by the
authors’ data, and that the observation of a discrete BM MC
population should not be viewed as a specific diagnostic
criterion for SM. In turn, the recommendations reported in
the literature for sensitive flow cytometric evaluation of BM
MCs should be strictly followed to prevent false-negative
results in the flow cytometry immunophenotypic diagnostic
workup of SM patients.
Laura Sánchez-Muñoz, MD, PhD
Jose Mario T. Morgado, MSc
Ivan Alvarez-Twose, MD
Almudena Matito, MD
Luis Escribano, MD, PhD
Instituto de Estudios de Mastocitosis de Castilla La Mancha
Hospital Virgen del Valle
Toledo, Spain
Cristina Teodosio, MSc
María Jara-Acevedo, MSc
Andrés C. García-Montero, PhD
Andrea Mayado, PhD
Alberto Orfao, MD, PhD
Servicio General de Citometría
Universidad de Salamanca
Salamanca, Spain
References
1. Pozdnyakova O, Kondtratiev S, Li B, et al. High-sensitivity
flow cytometric analysis for the evaluation of systemic mastocytosis including the identification of a new flow cytometric
criterion for bone marrow involvement. Am J Clin Pathol.
2012;138:416-424.
2. Escribano L, García Montero AC, Núñez R, et al. Flow cytometric analysis of normal and neoplastic mast cells: role in
diagnosis and follow-up of mast cell disease. Immunol Allergy
Clin North Am. 2006;26:535-547.
3. Akin C, Fumo G, Yavuz AS, et al. A novel form of mastocytosis associated with a transmembrane c-kit mutation and
response to imatinib. Blood. 2004;103:3222-3225.
4. García-Montero AC, Jara-Acevedo M, Teodosio C, et al. KIT
mutation in mast cells and other bone marrow haematopoietic
cell lineages in systemic mast cell disorders: a prospective study
of the Spanish Network on Mastocytosis (REMA) in a series
of 113 patients. Blood. 2006;108:2366-2372.
The Authors’ Reply
We would like to respond to the points raised by
Sánchez-Muñoz et al regarding our article.
First, there are no inconsistencies between the number of
patients with systemic mastocytosis (SM) and the number of
analyzed specimens. The study included 23 patients with SM.
However, 5 patients with SM had sequential flow cytometric
studies. Because each sample was analyzed as a separate
event, that resulted in a total of 39 SM specimens. Cases of
monoclonal mast cell activation syndrome (MMCAS) were
analyzed separately. Treatment information was beyond the
scope of the study.
Second, we would like to point out that the presence
of mast cell clusters by flow cytometry was 100% specific;
no false-positive results were observed. All cases with mast
cell clusters fulfilled the diagnostic criteria for SM based on
biopsy findings and/or other laboratory findings. Discrete
populations of mast cells were not observed in cases of
MMCAS, cutaneous mastocytosis, anaphylaxis, or mast cell
activation syndrome. We performed additional analyses of
cases of Waldenström macroglobulinemia (WM; n = 23),
406
Am J Clin Pathol 2013;139:404-407
5. Sánchez-Muñoz L, Alvarez-Twose I, García-Montero AC,
et al. Evaluation of the WHO criteria for the classification of
patients with mastocytosis. Mod Pathol. 2011;24:1157-1168.
6. Escribano L, Diaz-Agustin B, López A, et al.
Immunophenotypic analysis of mast cells in mastocytosis:
when and how to do it. Proposals of the Spanish Network
on Mastocytosis (REMA). Cytometry B Clin Cytom.
2004;58B:1-8.
7. Sánchez-Muñoz L, Teodosio C, Morgado JM, et al.
Immunophenotypic characterization of bone marrow mast
cells in mastocytosis and other mast cell disorders. Methods
Cell Biol. 2011;103:333-359.
8. Morgado JM, Sánchez-Muñoz L, Teodosio CG, et al.
Immunophenotyping in systemic mastocytosis diagnosis:
“CD25 positive” alone is more informative than the “CD25
and/or CD2” WHO criterion. Mod Pathol. 2012;25:516-521.
myelodysplastic syndrome (MDS; n = 10), and recovering
marrow (n = 3), and similarly, none of these cases showed
clustering of mast cells or aberrant CD25/CD2 expression.
Sánchez-Muñoz et al wonder whether the presence of
a discrete mast cell population on side-scatter and CD117
plots may just reflect an increased number of mast cells in
the sample. Based on our findings, this is not the case. For
example, in representative specimens from patients with SM,
MMCAS, anaphylaxis, and WM with a comparable number
of events in the CD117 gate ❚Figure 1❚, mast cell clustering
is present only in the case of SM, with the number of events
in the CD117 gate as low as 396. In cases of MMCAS (304
events in the CD117 gate), WM (996 events in the CD117
gate), MDS (427 events in the CD117 gate), recovering
marrow (304 events in the CD117 gate), and anaphylaxis
(450 events in the CD117 gate), the cells in the CD117
gate are scattered without cluster formation. In their letter,
the authors show 2 representative dot plots from patients
with SM and MDS; both images demonstrate clustering of
mast cells with side scatter and CD117 characteristics of “a
© American Society for Clinical Pathology
Correspondence
MMCAS
304 events
Anaphylaxis
250
200
200
200
150
100
50
10
2
3
4
WM
150
100
50
0
5
10
10
10
CD117 PE-A
SSC (×1,000)
250
0
996 events
10
2
3
4
100
50
250
200
200
200
100
50
0
10
2
3
4
5
10
10
10
CD117 PE-A
SSC (×1,000)
250
150
100
50
0
10
2
3
4
5
10
10
10
CD117 PE-A
10
2
3
4
10
10
10
CD117 PE-A
Recovering
marrow
427 events
250
150
450 events
150
0
5
10
10
10
CD117 PE-A
MDS
SSC (×1,000)
SSC (×1,000)
396 events
250
SSC (×1,000)
SSC (×1,000)
Systemic
mastocytosis
5
304 events
150
100
50
0
10
2
3
4
10
10
10
CD117 PE-A
5
❚Figure 1❚ Mast cell flow cytometric analysis in representative samples. The number of events indicates CD117 bright mast
cells to the right of the dotted line. MDS, myelodysplastic syndrome; MMCAS, monoclonal mast cell activation syndrome;
PE, phycoerythrin; SSC, side scatter; WM, Waldenström macroglobulinemia.
discrete population” that we believe to be a phenomenon of
SM. Although the authors state that these findings merely
represent an increased number of mast cells, on the basis
of our experience, in which no mast cell clustering was
observed in cases of MDS, we wonder whether the case
shown in their Figure 1B may represent a case of SM with
associated clonal hematologic non–mast cell lineage disease.
Finally, in our study, we observed a number of SM
cases that did not demonstrate aberrant CD25 and/or CD2
expression. All these cases met the diagnostic criteria for
SM based on biopsy and other laboratory findings. Although
absence of aberrant CD25, CD2 staining by flow cytometry
might be explained by lower sensitivity of the fluorochromes
employed, these CD25–, CD2– cases may indeed represent
a well-differentiated SM variant, as suggested by SánchezMuñoz et al. Interestingly, in contrast to the study by
Morgado et al,1 which showed that aberrant CD25 expression
alone is more informative than CD25 and/or CD2 expression,
we identified 2 cases of SM that demonstrated CD2 as the
sole aberrant marker in our study.
In conclusion, the phenomenon of mast cell clustering
is specific for systemic mastocytosis in our experience but
requires confirmation at other institutions.
Olga Pozdnyakova, MD, PhD
David M. Dorfman, MD, PhD
Department of Pathology
Brigham and Women’s Hospital
Harvard Medical School
Boston, MA
Reference
1. Morgado JM, Sánchez-Muñoz L, Teodosio CG, et al.
Immunophenotyping in systemic mastocytosis diagnosis:
“CD25 positive” alone is more informative than the “CD25
and/or CD2” WHO criterion. Mod Pathol. 2012;25:516-521.
© American Society for Clinical Pathology
Am J Clin Pathol 2013;139:404-407 407