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WHO Classification of Tumours
Mastocytosis


Definition
Mastocytosis is due to a clonal, neoplastic proliferation of mast cells that accumulate in one or more organ systems. It is characterized by the presence of multifocal compact clusters or cohesive aggregates/ infiltrates of abnormal mast cells. The disorder is heterogeneous, ranging from skin lesions that may spontaneously regress to highly aggressive neoplasms associated with multiorgan failure and short survival. Subtypes of mastocytosis are recognized mainly by the distribution of the disease and clinical manifestations (Table 2.09). In cutaneous mastocytosis (CM), the mast cell infiltration remains confined to the skin, whereas systemic mastocytosis (SM) is characterized by involvement of at least one extracutaneous organ with or without evidence of skin lesions. Masto­cytosis should be strictly separated from mast cell hyperplasia or mast cell activation states without morphological and/or molecular abnormalities that characterize the neoplastic proliferation. The criteria for the diagnosis of cutaneous and systemic mastocytosis is in found in Table 2.10.

Epidemiology
Mastocytosis may occur at any age. Cutaneous mastocytosis is most common in children and may be present at birth. About 50% of afflicted children develop typical skin lesions before 6 months of age. In adults, CM is less frequently diagnosed than in children

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Soter NA (2000)
Mastocytosis and the skin.
Hematol Oncol Clin North Am 14: 537-55, vi




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Wolff K, Komar M, Petzelbauer P (2001)
Clinical and histopathological aspects of cutaneous mastocytosis.
Leuk Res 25: 519-28



. A slight male predominance has been reported in CM. SM is generally diagnosed after the second decade of life; the male to female ratio has been reported to vary from 1:1 to 1:3
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Beltrani G, Carlesimo OA (1966)
[Telangiectasia macularis eruptiva perstans with mastocytosis].
Minerva Dermatol 41: 436-42




Click to access Pubmed
Metcalfe DD (1991)
Classification and diagnosis of mastocytosis: current status.
J Invest Dermatol 96: 2S-4S




Click to access Pubmed
Parwaresch MR, Horny HP, Lennert K (1985)
Tissue mast cells in health and disease.
Pathol Res Pract 179: 439-61



.

Sites of involvement
Approximately 80% of patients with masto­cytosis have evidence of skin involvement

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Pardanani A, Akin C, Valent P (2006)
Pathogenesis, clinical features, and treatment advances in mastocytosis.
Best Pract Res Clin Haematol 19: 595-615



. In SM the bone marrow (BM) is almost always involved, so morpho­logical and molecular analysis of a BM biopsy specimen is strongly recommended to confirm or exclude the diagnosis of SM
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Brunning RD, McKenna RW (1994)
Mast cell disease.
In: Atlas of tumor pathology. Tumors of the bone marrow, Vol. 3rd series. Armed Forces Institute of Pathology: Washington, D.C.: pp 419–434.




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Brunning RD, McKenna RW, Rosai J, Parkin JL, Risdall R (1983)
Systemic mastocytosis. Extracutaneous manifestations.
Am J Surg Pathol 7: 425-38




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Horny HP, Parwaresch MR, Lennert K (1985)
Bone marrow findings in systemic mastocytosis.
Hum Pathol 16: 808-14




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Lennert K, Parwaresch MR (1979)
Mast cells and mast cell neoplasia: a review.
Histopathology 3: 349-65



. Rarely, the peripheral blood (PB) shows leukaemia due to significant numbers of circulating mast cells
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Horny HP, Ruck M, Wehrmann M, Kaiserling E (1990)
Blood findings in generalized mastocytosis: evidence of frequent simultaneous occurrence of myeloproliferative disorders.
Br J Haematol 76: 186-93




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Miranda RN, Esparza AR, Sambandam S, Medeiros LJ (1994)
Systemic mast cell disease presenting with peripheral blood eosinophilia.
Hum Pathol 25: 727-30



. Other organs that may be involved in SM include the spleen, lymph nodes, liver and gastrointestinal tract mucosa, but any tissue may be affected
Click to access Pubmed
Brunning RD, McKenna RW (1994)
Mast cell disease.
In: Atlas of tumor pathology. Tumors of the bone marrow, Vol. 3rd series. Armed Forces Institute of Pathology: Washington, D.C.: pp 419–434.




Click to access Pubmed
Horny HP, Kaiserling E, Campbell M, Parwaresch MR, Lennert K (1989)
Liver findings in generalized mastocytosis. A clinicopathologic study.
Cancer 63: 532-8




Click to access Pubmed
Horny HP, Kaiserling E, Parwaresch MR, Lennert K (1992)
Lymph node findings in generalized mastocytosis.
Histopathology 21: 439-46




Click to access Pubmed
Horny HP, Ruck MT, Kaiserling E (1992)
Spleen findings in generalized mastocytosis. A clinicopathologic study.
Cancer 70: 459-68




Click to access Pubmed
Lennert K, Parwaresch MR (1979)
Mast cells and mast cell neoplasia: a review.
Histopathology 3: 349-65




Click to access Pubmed
Longley J, Duffy TP, Kohn S (1995)
The mast cell and mast cell disease.
J Am Acad Dermatol 32: 545-61; quiz 562-4




Click to access Pubmed
Metcalfe DD (1991)
The liver, spleen, and lymph nodes in mastocytosis.
J Invest Dermatol 96: 45S-46S




Click to access Pubmed
Parwaresch MR, Horny HP, Lennert K (1985)
Tissue mast cells in health and disease.
Pathol Res Pract 179: 439-61



. Skin lesions occur in more than 50% of SM patients, and are more often observed in those with an indolent course. In contrast, aggressive variants of SM often present without skin lesions
Click to access Pubmed
Horny HP, Parwaresch MR, Lennert K (1985)
Bone marrow findings in systemic mastocytosis.
Hum Pathol 16: 808-14



. However, some SM patients without skin lesions may on occasion present with an indolent form of SM, most often isolated BM mastocytosis.

Clinical features
Cutaneous mastocytosis includes several distinct clinico-histopathological entities (Table 2.11). Lesions of all forms of CM may urticate when stroked ("Darier’s sign") and most show intraepidermal accumulation of melanin pigment. The term "urticaria pigmentosa" macroscopically describes these two clinical features. Blistering ("bullous mastocytosis") does not represent a separate subtype but rather an exaggeration of urticaria. Blistering is usually seen in patients less than 3 years of age, and may be associated with all forms of paediatric CM

Click to access Pubmed
Pardanani A, Akin C, Valent P (2006)
Pathogenesis, clinical features, and treatment advances in mastocytosis.
Best Pract Res Clin Haematol 19: 595-615




Click to access Pubmed
Soter NA (2000)
Mastocytosis and the skin.
Hematol Oncol Clin North Am 14: 537-55, vi




Click to access Pubmed
Wolff K, Komar M, Petzelbauer P (2001)
Clinical and histopathological aspects of cutaneous mastocytosis.
Leuk Res 25: 519-28



.

Symptoms in SM at presentation have been grouped into 4 categories: 1) constitutional symptoms (fatigue, weight loss, fever, diaphoresis), 2) skin manifestations (pruritus, urticaria, dermatographism), 3) mediator-related systemic events (abdominal pain, gastrointestinal distress, flushing, syncope, headache, hypotension, tachycardia, respiratory symptoms) and 4) musculoskeletal complaints (bone pain, osteopenia/osteoporosis, fractures, arthralgias, myalgias)

Click to access Pubmed
Beltrani G, Carlesimo OA (1966)
[Telangiectasia macularis eruptiva perstans with mastocytosis].
Minerva Dermatol 41: 436-42




Click to access Pubmed
Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



. These symptoms range from mild in many patients to severe, life-threatening mediator-related events in others. Symptoms may also be related to organ impairment (due to mast cell infiltrates), particularly in patients with high-grade aggressive or leukaemic disease variants (Table 2.12).

Physical findings in SM at diagnosis may include splenomegaly (often minimal), while lymphadenopathy and hepatomegaly are found at significantly lower frequencies

Click to access Pubmed
Horny HP, Kaiserling E, Campbell M, Parwaresch MR, Lennert K (1989)
Liver findings in generalized mastocytosis. A clinicopathologic study.
Cancer 63: 532-8




Click to access Pubmed
Horny HP, Kaiserling E, Parwaresch MR, Lennert K (1992)
Lymph node findings in generalized mastocytosis.
Histopathology 21: 439-46




Click to access Pubmed
Horny HP, Ruck MT, Kaiserling E (1992)
Spleen findings in generalized mastocytosis. A clinicopathologic study.
Cancer 70: 459-68




Click to access Pubmed
Lennert K, Parwaresch MR (1979)
Mast cells and mast cell neoplasia: a review.
Histopathology 3: 349-65




Click to access Pubmed
Metcalfe DD (1991)
The liver, spleen, and lymph nodes in mastocytosis.
J Invest Dermatol 96: 45S-46S



. Organo­megaly is often absent in the most common variant, indolent systemic masto­cytosis (ISM), but is usually present, along with impaired organ function, in aggressive systemic mastocytosis (ASM) and in leukaemic variants. Severe systemic symptoms may occur in patients with ISM following extensive release and generation of biochemical mediators including histamine, eicosanoids, proteases and heparin. For example, gastrointestinal symptoms such as peptic ulcer disease or diarrhoea are more commonly attributed to release of biologically active mediators than to ­infiltration of the gastro­intestinal tract by excessive numbers of abnormal mast cells
Click to access Pubmed
Beltrani G, Carlesimo OA (1966)
[Telangiectasia macularis eruptiva perstans with mastocytosis].
Minerva Dermatol 41: 436-42




Click to access Pubmed
Longley J, Duffy TP, Kohn S (1995)
The mast cell and mast cell disease.
J Am Acad Dermatol 32: 545-61; quiz 562-4




Click to access Pubmed
Valent P, Akin C, Sperr WR, Horny HP, Arock M, Lechner K, Bennett JM, Metcalfe DD (2003)
Diagnosis and treatment of systemic mastocytosis: state of the art.
Br J Haematol 122: 695-717



.

Haematological abnormalities in SM include anaemia, leukocytosis, blood eosinophilia (a frequent finding), neutropenia, and thrombocytopenia

Click to access Pubmed
Bain BJ (2004)
Relationship between idiopathic hypereosinophilic syndrome, eosinophilic leukemia, and systemic mastocytosis.
Am J Hematol 77: 82-5




Click to access Pubmed
Brunning RD, McKenna RW (1994)
Mast cell disease.
In: Atlas of tumor pathology. Tumors of the bone marrow, Vol. 3rd series. Armed Forces Institute of Pathology: Washington, D.C.: pp 419–434.




Click to access Pubmed
Florian S, Esterbauer H, Binder T, Müllauer L, Haas OA, Sperr WR, Sillaber C, Valent P (2006)
Systemic mastocytosis (SM) associated with chronic eosinophilic leukemia (SM-CEL): detection of FIP1L1/PDGFRalpha, classification by WHO criteria, and response to therapy with imatinib.
Leuk Res 30: 1201-5




Click to access Pubmed
Horny HP, Parwaresch MR, Lennert K (1985)
Bone marrow findings in systemic mastocytosis.
Hum Pathol 16: 808-14




Click to access Pubmed
Klion AD, Noel P, Akin C, Law MA, Gilliland DG, Cools J, Metcalfe DD, Nutman TB (2003)
Elevated serum tryptase levels identify a subset of patients with a myeloproliferative variant of idiopathic hypereosinophilic syndrome associated with tissue fibrosis, poor prognosis, and imatinib responsiveness.
Blood 101: 4660-6




Click to access Pubmed
Pardanani A, Akin C, Valent P (2006)
Pathogenesis, clinical features, and treatment advances in mastocytosis.
Best Pract Res Clin Haematol 19: 595-615



. Bone marrow failure is encountered only in patients with aggressive or leukaemic disease variants. Significant numbers of circulating mast cells are rarely observed and are suggestive of mast cell leukaemia
Click to access Pubmed
Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



. In up to 30% of cases with SM, an associated, clonal haematological, non-mast cell lineage disease (AHNMD) is diagnosed before, simultaneously with, or after the diagnosis of SM. In principle, any defined myeloid or lymphatic malignancy may occur as the AHNMD, but myeloid neoplasms predominate, and chronic myelomonocytic leukaemia (CMML) is most common
Click to access Pubmed
Horny HP, Parwaresch MR, Lennert K (1985)
Bone marrow findings in systemic mastocytosis.
Hum Pathol 16: 808-14




Click to access Pubmed
Horny HP, Sotlar K, Sperr WR, Valent P (2004)
Systemic mastocytosis with associated clonal haematological non-mast cell lineage diseases: a histopathological challenge.
J Clin Pathol 57: 604-8




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Sotlar K, Fridrich C, Mall A, Jaussi R, Bültmann B, Valent P, Horny HP (2002)
Detection of c-kit point mutation Asp-816 --> Val in microdissected pooled single mast cells and leukemic cells in a patient with systemic mastocytosis and concomitant chronic myelomonocytic leukemia.
Leuk Res 26: 979-84




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Sperr WR, Walchshofer S, Horny HP, Födinger M, Simonitsch I, Fritsche-Polanz R, Schwarzinger I, Tschachler E, Sillaber C, Hagen W, Geissler K, Chott A, Lechner K, Valent P (1998)
Systemic mastocytosis associated with acute myeloid leukaemia: report of two cases and detection of the c-kit mutation Asp-816 to Val.
Br J Haematol 103: 740-9




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Stellmacher F, Sotlar K, Balleisen L, Valent P, Horny HP (2004)
Bone marrow mastocytosis associated with IgM kappa plasma cell myeloma.
Leuk Lymphoma 45: 801-5




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Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



. In patients with SM-AHNMD, clinical symptoms and disease course relate both to the associated haematological disorder and to SM
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Schwartz LB, Sakai K, Bradford TR, Ren S, Zweiman B, Worobec AS, Metcalfe DD (1995)
The alpha form of human tryptase is the predominant type present in blood at baseline in normal subjects and is elevated in those with systemic mastocytosis.
J Clin Invest 96: 2702-10




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Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



.

Serum tryptase levels are used in the evaluation and monitoring of patients with mastocytosis. The finding of a persistently elevated serum total tryptase >20 ng/mL is suggestive of SM and is used as a "minor" criterion for diagnosis, unless there is an associated clonal myeloid non-mast cell disorder, in which case this parameter is not valid. Serum tryptase levels are normal to slightly elevated in most patients with CM and have also been found to be independent of the patient’s tryptase ­haplotype

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Schwartz LB, Sakai K, Bradford TR, Ren S, Zweiman B, Worobec AS, Metcalfe DD (1995)
The alpha form of human tryptase is the predominant type present in blood at baseline in normal subjects and is elevated in those with systemic mastocytosis.
J Clin Invest 96: 2702-10




Click to access Pubmed
Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



.

Morphology
The diagnosis of mastocytosis requires demonstration of multifocal clusters or cohesive aggregates/infiltrates of mast in adequate biopsy specimens (Table 2.10). The histological pattern of the mast cell infiltrate may vary according to the tissue sampled

Click to access Pubmed
Bain BJ (2004)
Relationship between idiopathic hypereosinophilic syndrome, eosinophilic leukemia, and systemic mastocytosis.
Am J Hematol 77: 82-5




Click to access Pubmed
Brunning RD, McKenna RW, Rosai J, Parkin JL, Risdall R (1983)
Systemic mastocytosis. Extracutaneous manifestations.
Am J Surg Pathol 7: 425-38




Click to access Pubmed
Florian S, Esterbauer H, Binder T, Müllauer L, Haas OA, Sperr WR, Sillaber C, Valent P (2006)
Systemic mastocytosis (SM) associated with chronic eosinophilic leukemia (SM-CEL): detection of FIP1L1/PDGFRalpha, classification by WHO criteria, and response to therapy with imatinib.
Leuk Res 30: 1201-5




Click to access Pubmed
Horny HP, Kaiserling E, Campbell M, Parwaresch MR, Lennert K (1989)
Liver findings in generalized mastocytosis. A clinicopathologic study.
Cancer 63: 532-8




Click to access Pubmed
Horny HP, Kaiserling E, Parwaresch MR, Lennert K (1992)
Lymph node findings in generalized mastocytosis.
Histopathology 21: 439-46




Click to access Pubmed
Horny HP, Ruck MT, Kaiserling E (1992)
Spleen findings in generalized mastocytosis. A clinicopathologic study.
Cancer 70: 459-68




Click to access Pubmed
Klion AD, Noel P, Akin C, Law MA, Gilliland DG, Cools J, Metcalfe DD, Nutman TB (2003)
Elevated serum tryptase levels identify a subset of patients with a myeloproliferative variant of idiopathic hypereosinophilic syndrome associated with tissue fibrosis, poor prognosis, and imatinib responsiveness.
Blood 101: 4660-6




Click to access Pubmed
Metcalfe DD (1991)
The liver, spleen, and lymph nodes in mastocytosis.
J Invest Dermatol 96: 45S-46S



. A diffuse interstitial infiltration pattern is defined as loosely scattered mast cells in the absence of compact aggregates. It must be noted, however, that this pattern is also observed in reactive mast cell hyperplasia and in cases of myelomastocytic leukaemia, a term used for cases with advanced myeloid neoplasms in whom elevated numbers of immature atypical mast cells are found, but criteria for SM are not met
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Sperr WR, Drach J, Hauswirth AW, Ackermann J, Mitterbauer M, Mitterbauer G, Foedinger M, Fonatsch C, Simonitsch-Klupp I, Kalhs P, Valent P (2005)
Myelomastocytic leukemia: evidence for the origin of mast cells from the leukemic clone and eradication by allogeneic stem cell transplantation.
Clin Cancer Res 11: 6787-92



. In patients with the diffuse infiltration pattern it is therefore impossible to establish the diagnosis of mastocytosis without additional studies including the demonstration of an aberrant immuno­phenotype and/or detection of an activating point mutation in KIT
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Horny HP, Valent P (2001)
Diagnosis of mastocytosis: general histopathological aspects, morphological criteria, and immunohistochemical findings.
Leuk Res 25: 543-51




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Horny HP, Valent P (2002)
Histopathological and immunohistochemical aspects of mastocytosis.
Int Arch Allergy Immunol 127: 115-7




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Krokowski M, Sotlar K, Krauth MT, Födinger M, Valent P, Horny HP (2005)
Delineation of patterns of bone marrow mast cell infiltration in systemic mastocytosis: value of CD25, correlation with subvariants of the disease, and separation from mast cell hyperplasia.
Am J Clin Pathol 124: 560-8




Click to access Pubmed
Sotlar K, Fridrich C, Mall A, Jaussi R, Bültmann B, Valent P, Horny HP (2002)
Detection of c-kit point mutation Asp-816 --> Val in microdissected pooled single mast cells and leukemic cells in a patient with systemic mastocytosis and concomitant chronic myelomonocytic leukemia.
Leuk Res 26: 979-84




Click to access Pubmed
Sotlar K, Horny HP, Simonitsch I, Krokowski M, Aichberger KJ, Mayerhofer M, Printz D, Fritsch G, Valent P (2004)
CD25 indicates the neoplastic phenotype of mast cells: a novel immunohistochemical marker for the diagnosis of systemic mastocytosis (SM) in routinely processed bone marrow biopsy specimens.
Am J Surg Pathol 28: 1319-25



. In contrast, the presence of multifocal compact mast cell infiltrates or a diffuse-compact mast cell infiltration pattern is highly compatible with the diagnosis of mastocytosis during first inspection. However, additional immuno­histochemical and molecular studies are strongly recommended even in these cases.

In tissue sections stained with H&E, normal/ reactive mast cells usually are loosely scattered throughout the sample, and ­display round to oval nuclei with clumped chromatin, a low nuclear/cytoplasmic ratio, and nucleoli that are absent or ­indistinct. The mast cell cytoplasm is abundant and usually filled with small, faintly visible granules. Dense aggregates of mast cells are only very exceptionally detected in reactive states or in patients treated with stem cell factor (SCF)

Click to access Pubmed
Lennert K, Parwaresch MR (1979)
Mast cells and mast cell neoplasia: a review.
Histopathology 3: 349-65




Click to access Pubmed
Parwaresch MR, Horny HP, Lennert K (1985)
Tissue mast cells in health and disease.
Pathol Res Pract 179: 439-61




Click to access Pubmed
Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



. In smear preparations, mast cells are readily visible in Romanowsky stains as medium-sized round or oval cells with plentiful cytoplasm, containing densely packed metachromatic granules and round or oval nuclei. In normal/reactive states, mast cells are easily distinguished from the smaller metachromatic basophils which have segmented nuclei, and larger and fewer granules. With enzyme cytochemistry, mast cells react strongly with naphthol-ASD-chloroacetate esterase (CAE) but do not express myeloperoxidase. In mastocytosis, the ­cytology of mast cells varies, but abnormal cytologic features are almost always detected, including marked spindling and hypogranularity
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Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



.

Cytomorphological atypia is pronounced in high-grade lesions of mastocytosis, with the occurrence of metachromatic blast cells being a usual feature of mast cell leukaemia

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Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



. The finding of frequent mast cells with bi- or multilobated nuclei ("promastocytes") usually indicates an aggressive mast cell proliferation, ­although these cells may be seen at low frequency in other subtypes of the disease
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Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



. Mitotic figures in mast cells do occur, but are infrequent even in the aggressive or leukaemic variants of SM.

To assess mast cell numbers with conventional staining procedures, Giemsa or toluidine blue are employed to detect the metachromatic mast cell granules and CAE is also helpful

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Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, Marone G, Nuñez R, Akin C, Sotlar K, Sperr WR, Wolff K, Brunning RD, Parwaresch RM, Austen KF, Lennert K, Metcalfe DD, Vardiman JW, Bennett JM (2001)
Diagnostic criteria and classification of mastocytosis: a consensus proposal.
Leuk Res 25: 603-25



. However, the most specific methods for identification of immature or atypical mast cells in tissue sections utilize immunohisto­chemical staining for tryptase/chymase and CD117 and, for neoplastic mast cells, CD2 and CD25. The morphologic features of the common subtypes of mastocytosis are described below.


Classification of mastocytosis
Cutaneous mastocytosis
Systemic mastocytosis

> Variants of systemic mastocytosis
Indolent systemic mastocytosis
Systemic mastocytosis with associated clonal haematological non-mast-cell lineage disease
Aggressive systemic mastocytosis
Mast cell leukaemia
Mast cell sarcoma
Extracutaneous mastocytoma









Hans-Peter Horny
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Hans-Peter Horny
Institute of Pathology
Clinic of Ansbach
Ansbach
Germany




Dean D. Metcalfe
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Dean D. Metcalfe
Laboratory of Allergic Diseases, NIAID
National Institutes of Health
Bethesda
USA




John M. Bennett
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John M. Bennett
Departments of Medicine and Pathology
University of Rochester Medical Center and the James P. Wilmot Cancer Center
Rochester
USA




Barbara J. Bain
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Barbara J. Bain
Department of Haematology
Imperial College Faculty of Medicine, St. Mary’s Hospital
London
UK




Cem Akin
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Cem Akin
Department of Internal Medicine
University of Michigan
Ann Arbor
USA




Luis Escribano
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Luis Escribano
Centro de Estudios de Mastocitosis de Castilla La Mancha
Hospital Virgen del Valle
Toledo
Spain




Peter Valent
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Peter Valent








Spindled-shaped mast cells in systemic mastocytosis.
Spindled-shaped mast cells in systemic mastocytosis.

Numerous reactive mast cells in a case of lymphoplasmacytic lymphoma.
Numerous reactive mast cells in a case of lymphoplasmacytic lymphoma.

Loosely scattered spindle-shaped mast cells in indolent systemic mastocytosis.
Loosely scattered spindle-shaped mast cells in indolent systemic mastocytosis.

 Immunostaining of neoplastic mast cells with CD25
Immunostaining of neoplastic mast cells with CD25

Metachromatic granules in mast cells in a case of systemic mastocytosis.
Metachromatic granules in mast cells in a case of systemic mastocytosis.

Atypical mast cell in an aspirate smear
Atypical mast cell in an aspirate smear

Variant mast cell morphology in systemic mastocytosis
Variant mast cell morphology in systemic mastocytosis

Perivascular mast cells: tryptase stain
Perivascular mast cells: tryptase stain

Perivascular mast cells: CD117
Perivascular mast cells: CD117

Perivascular mast cells: CD25
Perivascular mast cells: CD25