Diagnostic Workup for Advanced Forms of Mastocytosis

Wolfgang R. Sperr1, Celalettin Ustun2

1Department of Internal Medicine I, Division of Hematology and Hemostaseology, Medical University of Vienna, Vienna, Austria

2Division of Hematology, Oncology and Transplantation, Department of Medicine, University of Minnesota, Minnesota, USA

Author Contact:

Wolfgang Sperr, MD:  wolfgang.r.sperr@meduniwien.ac.at

Celalettin Ustun, MD:  custun@umn.edu

Mastocytosis denotes a heterogeneous group of disorders characterized by abnormal growth and accumulation of mast cells (MCs) that has a variable prognosis and course of disease. In contrast to adults, childhood mastocytosis often resolves spontaneously before adolescence or young adulthood.1, 2 Most systemic mastocytosis (SM) variants diagnosed in adults show a stable clinical course over decades and do not decrease the life span.3 The World Health Organization (WHO) criteria separates cutaneous, indolent and advanced forms. Advanced variants of mastocytosis include aggressive systemic mastocytosis (ASM), mast cell leukemia (MCL), and SM with an associated hematologic non mast cell lineage disorder (SM-AHNMD), a term that was shortened in the 2016 revision of the WHO classification for mastocytosis to “SM with an associated hematological neoplasm” (SM-AHN).1, 3, 4 The diagnosis of mastocytosis is established in a stepwise approach, using WHO major and minor criteria (with one major and one minor or at least three minor criteria having to be fulfilled).1 The major criterion is multifocal mast cell infiltration in the bone marrow (BM) or in an extracutaneous organ, as assessed by histology.3, 5 Minor SM criteria relate to the morphology of mast cells (histology and/or cytology), their cell surface markers (aberrant expression of CD2 and/or CD25), molecular findings (KIT mutation at codon 816), and serum tryptase level (>20 ng/ml) (Figure 1).6 To diagnose an advanced form of mastocytosis, the presence of B-findings, C-findings, or an AHN is of importance (Table 1, Figure 1). In patients with two or more B-findings the diagnosis of smoldering systemic mastocytosis (SSM) can be established.7 C-findings (one is enough to diagnose aggressive SM) are indicative of ASM or MCL.1, 5, 7 It is of particular importance that organ damage caused by MC infiltration only counts as an SM-related C-finding.1, 5, 7, 8 In case of suspected AHN, further markers and criteria to classify the AHN according to WHO criteria have to be applied to fully diagnose both the SM component and the AHN component of the disease and to identify potential drug targets.1, 3, 5, 8

Figure 1. Stepwise approach to diagnosis of systemic mastocytosis variants using World Health Organization Criteria

Table 1. B– and C-findings in advanced SM

B-FINDINGS (borderline ‘benign’)*:C-FINDINGS (C, critical):
Infiltration grade in BM (focal dense MC-infiltrates) >30% and serum tryptase level >200 ng/mlSigns of dysplasia or myeloproliferation in non-mast cell lineage compartments of the BM, but no AHN; blood counts normal or only slightly abnormalHepatomegaly without impairment of liver function (no ascites) and/or splenomegaly and/or lymphadenopathy (palpable >2 cm on Ultrasound/CT)Abnormal myelopoiesis with abnormal blood counts, but no frank AHNHepatomegaly with impairment of liver function (ascites)Splenomegaly with hypersplenism (splenic dysfunction)Malabsorption and weight loss due to GI-tract MC infiltratesSkeletal involvement with large osteolyses and/or pathologic fracturesOther organ systems affected by MC-infiltrates with associated impairment of organ function

*Two or more B-findings, with the absence of C-findings, must be present to diagnose smoldering systemic mastocytosis.

†One or more C-findings must be present to diagnose aggressive systemic mastocytosis.

Clinical findings       

The presence or absence of skin lesions can be an important clinical finding. Patients with ASM or MCL may or may not have skin lesions, with less than 50% of those with MCL presenting with cutaneous involvement.9 This is in contrast to patients with ISM or SSM, the majority of whom present with typical skin lesions.9 Therefore, the absence of skin lesions may be suggestive of aggressive disease variants. However, the absence of skin lesions is not confined to advanced variants. In bone marrow mastocytosis (BMM), a sub-variant of ISM, no skin lesions are detectable, and the prognosis is excellent.5 Indeed, it has been recently estimated that 5% of patients with ISM may also present without skin lesions.9

Another observation of importance is weight loss. Together with hypoalbuminemia, it is indicative of mast cell-induced organ damage and thus is a C-finding.5

An additional typical finding in SM is symptoms caused by the release of mast cell mediators, including histamine, cytokines, and leukotrienes.5 Related symptoms are headache, flushing, pruritus, diarrhea, hypotension, and bone pain. Excessive mast cell mediator release may lead to anaphylaxis in patients with mastocytosis. However, such symptoms can occur in all patients with SM and must not be misinterpreted as signs of advanced SM.5

Peripheral blood findings

Elevated serum tryptase is the key finding in patients with SM. Moreover, tryptase may serve as a surrogate marker to estimate the aggressiveness of the disease.6 Likewise, very high tryptase levels (>200 ng/ml) represent a B finding necessary to diagnose SSM.1, 3, 5, 8 In ASM and MCL the majority of patients present with highly elevated serum tryptase levels.5 However, a moderate elevated serum tryptase does not exclude advanced SM.10 Another important aspect is that tryptase must not be counted as SM criterion when the patient has an AHN, because tryptase can also be expressed in neoplastic myeloid cells or immature basophils.11 Tryptase measurement is also of importance for the monitoring of SM.

Many patients with advanced SM present with abnormal peripheral blood counts.1 Peripheral blood counts also help to differentiate between different variants of advanced SM.1 Whereas in SSM, the blood counts are within the normal range or slightly abnormal (B-finding), patients with ASM and MCL typically have decreased numbers of cells in the peripheral blood, including granulocytes <1.0 G/L, and/or hemoglobin <10 g/dl, and/or platelets <100 x 109/L.1 The presence of >10% MCs in the peripheral blood denotes MCL.1 An increase in the numbers of eosinophil granulocytes is another characteristic finding of advanced disease. An abnormal blood count is also a key finding to detect an AHN and to diagnose SM-AHN.1

With respect to laboratory chemistry, albumin is an important marker. Decreased albumin levels may be a sign of impaired liver function, in particular when observed together with elevated liver enzymes, enlarged liver, or signs of elevated pressure in the portal vein, like fluid in the abdominal cavity.1, 3, 5, 7 The combination of these findings can be indicative of progressive destruction of the liver by mast cell infiltrates.1, 3, 5 Typically, alkaline phosphatase is elevated in such patients, as well.1, 3, 5, 7, 8 On the other hand as stated above, hypoalbuminemia is also a sign for malabsorption. Both progressive destruction of the liver by mast cell infiltrates and malabsorption are C-findings necessary to diagnose ASM or MCL.1, 7

ß2-microglobulin is a well-established prognostic marker in patients with lymphomas. In these disorders, an elevated level reflects a high tumor burden. In patients with SM, the ß2-microglobulin level was found to be of prognostic significance, predicting an unfavorable outcome.12 In this regard, one could speculate that involvement of the lymphocytic cells in SM might be associated with progression of disease. However, confirming studies are warranted to determine the impact of lymphocytic involvement and the prognostic value of ß2-microglobulin.

Tissue Biopsies

Although the presence of the major criterion for diagnosis of SM can be evaluated with a biopsy from any organ involved in disease other than skin (e.g., liver, gastrointestinal tract),13, 14 bone marrow is the most common site.15 There are many pros of a bone marrow biopsy/aspirate, including providing information on an AHN, rendering differential diagnosis with other possible malignancies, and being easy and safe.

MCs infiltration can be diffuse or multifocal in the bone marrow. MCs can be morphologically round, oval or spindle shaped.16 Immunohistochemistry and flow cytometric analyses (e.g., looking at cell markers) for CD33, CD43, CD68, CD117 (KIT), and tryptase should be performed in the tissue. Neoplastic MCs also express aberrant CD217 and/or CD25.  Evaluation of bone marrow biopsy and aspirate is also critical for minor diagnostic criteria: the presence and increase of spindle shaped/atypical MCs (≥25%), the expression of CD2, CD25, or both, in MCs, and presence of the KIT D816V mutation.16

Moreover, a bone marrow biopsy is important to make a differential diagnosis between the variants of advanced SM. For example, although in ASM, dense sheets of MCs in the bone marrow biopsy are seen, if MCs constitute ³20% of all nucleated cells in bone marrow aspirate smears, it is defined as MCL.1 (MCL can be aleukemic if there are no circulating MCs in peripheral blood.18) In SM-AHN, the AHN component1 can be a myeloid malignancy [acute myelogenous leukemia (in particular t(8;21), chronic myelomonocytic leukemia, myeloproliferative neoplasias (very rarely chronic myelogenous leukemia), myelodysplastic syndrome] or plasma/lymphoid malignancies including, chronic lymphocytic leukemia, lymphomas, or plasma cell malignancies (myeloma). Sometimes, hematologic malignancies with severe, diffuse bone marrow infiltration (e.g., acute myelogenous leukemia) can obscure MCs that can be more apparent in the remission bone marrow biopsies after chemotherapy (i.e., occult mastocytosis).19 Osteosclerosis (“thick, tough bones” that can make performing a bone marrow biopsy technically difficult) is also readily detected in bone marrow biopsies.14

Other entities: mast cell sarcoma is a rare and aggressive tumor, but almost always involves extramedullary organs.20 There are also tryptase positive aggressive hematologic malignancies that should be differentiated from advanced SM.21, 22

Ultrasound, X-Ray, and Densitometry

In all patients with SM, bone densitometry should be included in the diagnostic work up and repeated periodically to detect early osteoporosis.5, 8 In case of suspected advanced mastocytosis, the staging should include imaging of the skeletal system and ultrasound of the abdomen. Ultrasound of the abdomen may reveal enlargement of liver, spleen or lymph nodes, as well as fluid in the abdominal cavity.23 As already stated, these findings without impairment of organ function are indicative for SSM (B-findings). Together with signs of organ damage, these observations are C-findings. Imaging of the skeleton may disclose signs of osteoporosis, osteosclerosis, or focal areas of osteolyses.14, 24 In most cases, the osteolytic lesions are small in size (0.5 cm) and not accompanied by clinical symptoms. In a few cases, however, larger osteolyses with pathologic (spontaneous) fractures are found.23, 24

Molecular markers

The most important molecular marker to show monoclonality in SM is the KIT point mutation D816V that can be analyzed in the bone marrow and the peripheral blood.1, 25 In the majority of patients with SM, neoplastic MCs harbor this mutation.1 In particular, in >80% of patients with indolent systemic mastocytosis, SSM or SM-AHN, KIT D816V is detectable.8, 26 In contrast, the prevalence of KIT D816V is lower in ASM (>60%) and MCL.8, 26 In this regard, several points have to be discussed. Firstly, if KIT D816V is negative, patients could harbor other mutations at codon 816, including D816H or D816Y. To detect these mutations, further diagnostic work-up (i.e., the amplification of the codon 17 and sequencing) is important. Secondly, mutations can affect other regions of KIT like the juxtamembrane domain, transmembrane domain or extracellular domain. In these cases, next-generation sequencing should be considered.8, 26

Another interesting aspect is the KIT D816V allele burden. Recently is has been shown that the allele burden differs between disease variants. In patients with advanced SM, a high allele burden can be observed, in contrast to indolent disease or a cutaneous variant. Moreover, the allele burden at diagnosis is of importance for prognostication, follow-up, as well as for quantification of response to treatment.27

Of note, in a majority of patients with SM, KIT D816V is detectable and can occur in cutaneous mastocytosis as well.1, 3, 5, 8 Likewise, Bodemer et al. reported that a mutation in codon 816 (exon 17) can be detected in cutaneous lesions of pediatric mastocytosis patients in 42%, and outside exon 17 in 44%.26 This suggests that additional genetic alterations, together with KIT D816V, result in neoplastic proliferation of MCs in advanced SM and thus are responsible for consecutive organ destruction by mast cell infiltration. Indeed, as assessed by next-generation sequencing, additional molecular aberrations were identified in the majority of patients with advanced SM.28 The most frequently affected genes were TET2, SRSF2, ASXL1, CBL, RUNX and JAK2 (n = 11). With regard to overall survival, SRSF2 and ASXL1 were found to be independent predictive factors for a poor prognosis, in contrast to TET2, JAK2, or RUNX1. Moreover, the number of mutated genes of the panel SRSF2/ASXL1/RUNX1 was indicative for an inferior overall survival and adverse clinical characteristics.29

Diagnostic Work-up Summary:

Diagnostic work-up should include:

  • Careful history and physical exam
  • Serum tryptase
  • Bone marrow biopsy and aspirate with appropriate analyses, if serum tryptase is high and/or blood counts are abnormal
  • Molecular testing from bone marrow
  • Abdominal ultrasound
  • Dexa scan and/or other skeletal imaging
  • Endoscopies with biopsies in cases with gastrointestinal symptoms
  • Chest CT, in patients with pulmonary symptoms (very rarely)

Edited by

Denyse Nanan, MD, PhD

Valerie M. Slee, RN, BSN

Susan Jennings, PhD

The Mastocytosis Society, Inc.

  1. Valent P, Horny HP, Escribano L, Longley BJ, Li CY, Schwartz LB, et al. Diagnostic criteria and classification of mastocytosis: a consensus proposal. Leuk Res. 2001 Jul;25(7):603-25. http://www.ncbi.nlm.nih.gov/pubmed/11377686
  2. Meni C, Bruneau J, Georgin-Lavialle S, Le Sache de Peufeilhoux L, Damaj G, Hadj-Rabia S, et al. Paediatric mastocytosis: a systematic review of 1747 cases. Br J Dermatol. 2015 Mar;172(3):642-51. http://www.ncbi.nlm.nih.gov/pubmed/25662299
  3. Lim KH, Tefferi A, Lasho TL, Finke C, Patnaik M, Butterfield JH, et al. Systemic mastocytosis in 342 consecutive adults: survival studies and prognostic factors. Blood. 2009 Jun 4;113(23):5727-36. http://www.ncbi.nlm.nih.gov/pubmed/19363219
  4. Arber DA, Orazi A, Hasserjian R, Thiele J, Borowitz MJ, Le Beau MM, et al. The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood. 2016 May 19;127(20):2391-405. http://www.ncbi.nlm.nih.gov/pubmed/27069254
  5. Valent P, Sperr WR, Akin C. How I treat patients with advanced systemic mastocytosis. Blood. 2010 Dec 23;116(26):5812-7. http://www.ncbi.nlm.nih.gov/pubmed/20855864
  6. Schwartz LB, Metcalfe DD, Miller JS, Earl H, Sullivan T. Tryptase levels as an indicator of mast-cell activation in systemic anaphylaxis and mastocytosis. N Engl J Med. 1987 Jun 25;316(26):1622-6. http://www.ncbi.nlm.nih.gov/pubmed/3295549
  7. Sperr WR, Valent P. Diagnosis, progression patterns and prognostication in mastocytosis. Expert Rev Hematol. 2012 Jun;5(3):261-74. http://www.ncbi.nlm.nih.gov/pubmed/22780207
  8. Arock M, Valent P. Pathogenesis, classification and treatment of mastocytosis: state of the art in 2010 and future perspectives. Expert Rev Hematol. 2010 Aug;3(4):497-516. http://www.ncbi.nlm.nih.gov/pubmed/21083038
  9. Hartmann K, Escribano L, Grattan C, Brockow K, Carter MC, Alvarez-Twose I, et al. Cutaneous manifestations in patients with mastocytosis: Consensus report of the European Competence Network on Mastocytosis; the American Academy of Allergy, Asthma & Immunology; and the European Academy of Allergology and Clinical Immunology. J Allergy Clin Immunol. 2016 Jan;137(1):35-45. http://www.ncbi.nlm.nih.gov/pubmed/26476479
  10. Sperr WR, Escribano L, Jordan JH, Schernthaner GH, Kundi M, Horny HP, et al. Morphologic properties of neoplastic mast cells: delineation of stages of maturation and implication for cytological grading of mastocytosis. Leuk Res. 2001 Jul;25(7):529-36. http://www.ncbi.nlm.nih.gov/pubmed/11377677
  11. Sperr WR, El-Samahi A, Kundi M, Girschikofsky M, Winkler S, Lutz D, et al. Elevated tryptase levels selectively cluster in myeloid neoplasms: a novel diagnostic approach and screen marker in clinical haematology. Eur J Clin Invest. 2009 Oct;39(10):914-23. http://www.ncbi.nlm.nih.gov/pubmed/19522836
  12. Escribano L, Alvarez-Twose I, Sanchez-Munoz L, Garcia-Montero A, Nunez R, Almeida J, et al. Prognosis in adult indolent systemic mastocytosis: a long-term study of the Spanish Network on Mastocytosis in a series of 145 patients. J Allergy Clin Immunol. 2009 Sep;124(3):514-21. http://www.ncbi.nlm.nih.gov/pubmed/19541349
  13. Horny HP, Valent P. Diagnosis of mastocytosis: general histopathological aspects, morphological criteria, and immunohistochemical findings. Leuk Res. 2001 Jul;25(7):543-51. http://www.ncbi.nlm.nih.gov/pubmed/11377679
  14. Ustun C, Cayci Z, Courville E. A patient with skin lesions, osteosclerosis and hepatosplenomegaly. Br J Haematol. 2014 Nov;167(3):291. http://www.ncbi.nlm.nih.gov/pubmed/25039362
  15. Horny HP. Mastocytosis: an unusual clonal disorder of bone marrow-derived hematopoietic progenitor cells. Am J Clin Pathol. 2009 Sep;132(3):438-47. http://www.ncbi.nlm.nih.gov/pubmed/19687320
  16. George TI, Horny HP. Systemic mastocytosis. Hematol Oncol Clin North Am. 2011 Oct;25(5):1067-83, vii. http://www.ncbi.nlm.nih.gov/pubmed/22054735
  17. Sotlar K, Horny HP, Simonitsch I, Krokowski M, Aichberger KJ, Mayerhofer M, et al. 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. 2004 Oct;28(10):1319-25. http://www.ncbi.nlm.nih.gov/pubmed/15371947
  18. Valent P, Sotlar K, Sperr WR, Reiter A, Arock M, Horny HP. Chronic mast cell leukemia: a novel leukemia-variant with distinct morphological and clinical features. Leuk Res. 2015 Jan;39(1):1-5. http://www.ncbi.nlm.nih.gov/pubmed/25443885
  19. Johnson RC, Savage NM, Chiang T, Gotlib JR, Cherry AM, Arber DA, et al. Hidden mastocytosis in acute myeloid leukemia with t(8;21)(q22;q22). Am J Clin Pathol. 2013 Oct;140(4):525-35. http://www.ncbi.nlm.nih.gov/pubmed/24045550
  20. Monnier J, Georgin-Lavialle S, Canioni D, Lhermitte L, Soussan M, Arock M, et al. Mast cell sarcoma: new cases and literature review. Oncotarget. 2016 Oct 04;7(40):66299-309. http://www.ncbi.nlm.nih.gov/pubmed/27602777
  21. Valent P, Sperr WR, Sotlar K, Reiter A, Akin C, Gotlib J, et al. The serum tryptase test: an emerging robust biomarker in clinical hematology. Expert Rev Hematol. 2014 Oct;7(5):683-90. http://www.ncbi.nlm.nih.gov/pubmed/25169217
  22. Valent P, Escribano L, Broesby-Olsen S, Hartmann K, Grattan C, Brockow K, et al. Proposed diagnostic algorithm for patients with suspected mastocytosis: a proposal of the European Competence Network on Mastocytosis. Allergy. 2014 Oct;69(10):1267-74. http://www.ncbi.nlm.nih.gov/pubmed/24836395
  23. Avila NA, Ling A, Worobec AS, Mican JM, Metcalfe DD. Systemic mastocytosis: CT and US features of abdominal manifestations. Radiology. 1997 Feb;202(2):367-72. http://www.ncbi.nlm.nih.gov/pubmed/9015059
  24. Rafii M, Firooznia H, Golimbu C, Balthazar E. Pathologic fracture in systemic mastocytosis. Radiographic spectrum and review of the literature. Clin Orthop Relat Res. 1983 Nov(180):260-7. http://www.ncbi.nlm.nih.gov/pubmed/6354546
  25. Arock M, Sotlar K, Akin C, Broesby-Olsen S, Hoermann G, Escribano L, et al. KIT mutation analysis in mast cell neoplasms: recommendations of the European Competence Network on Mastocytosis. Leukemia. 2015 Jun;29(6):1223-32. http://www.ncbi.nlm.nih.gov/pubmed/25650093
  26. Bodemer C, Hermine O, Palmerini F, Yang Y, Grandpeix-Guyodo C, Leventhal PS, et al. Pediatric mastocytosis is a clonal disease associated with D816V and other activating c-KIT mutations. J Invest Dermatol. 2010 Mar;130(3):804-15. http://www.ncbi.nlm.nih.gov/pubmed/19865100
  27. Broesby-Olsen S, Kristensen T, Vestergaard H, Brixen K, Moller MB, Bindslev-Jensen C, et al. KIT D816V mutation burden does not correlate to clinical manifestations of indolent systemic mastocytosis. J Allergy Clin Immunol. 2013 Sep;132(3):723-8. http://www.ncbi.nlm.nih.gov/pubmed/23587333
  28. Schwaab J, Schnittger S, Sotlar K, Walz C, Fabarius A, Pfirrmann M, et al. Comprehensive mutational profiling in advanced systemic mastocytosis. Blood. 2013 Oct 3;122(14):2460-6. http://www.ncbi.nlm.nih.gov/pubmed/23958953
  29. Jawhar M, Schwaab J, Schnittger S, Meggendorfer M, Pfirrmann M, Sotlar K, et al. Additional mutations in SRSF2, ASXL1 and/or RUNX1 identify a high-risk group of patients with KIT D816V(+) advanced systemic mastocytosis. Leukemia. 2016 Jan;30(1):136-43. http://www.ncbi.nlm.nih.gov/pubmed/26464169
Skip to content