Systemic mastocytosis associated with t(8;21)(q22;q22) acute myeloid leukemia

Aggressive systemic mastocytosis with the co-occurrence of PRKG2::PDGFRB, KAT6A::NCOA2, and RXRA::NOTCH1 fusion transcripts and a heterozygous RUNX1 frameshift mutation

Systemic mastocytosis (SM) is a myeloproliferative neoplasm displaying abnormal mast cell proliferation. It is subdivided into different forms, including aggressive systemic mastocytosis (ASM) and systemic mastocytosis with an associated hematologic neoplasm (SM-AHN). Oncogenic genetic alterations include point mutations, mainly the KIT D816V, conferring poor prognosis and therapy resistance, and fusion genes, with those involving PDGFRA/PDGFRB as the most recurrent events. We here describe an ASM case negative to the KIT D816V and JAK2 V617F alterations but showing a RUNX1 frameshift heterozygous mutation and the co-occurrence of three fusion transcripts. The first one, PRKG2::PDGFRB, was generated by a balanced t(4;5)(q24;q32) translocation as the sole abnormality. Other two novel chimeras, KAT6A::NCOA2 and RXRA::NOTCH1, originated from cryptic intra-chromosomal abnormalities. The patient rapidly evolved towards SM-AHN, characterized by the persistence of the PRKG2::PDGFRB chimera, due to the presence of an extra copy of the der(5)t(4;5)(q24;q34) chromosome and an increase in the RUNX1 mutation allelic frequency. The results indicated that the transcriptional landscape and the mutational profile of SM deserve attention to predict the evolution and prognosis of this complex disease, whose classification criteria are still a matter of debate.

Systemic Mastocytosis with Associated Hematological Neoplasms. Diagnostic features and unique response pattern to tyrosine kinase inhibitors and allo-bone marrow transplantation therapy

Systemic Mastocytosis is a clonal proliferation of mast cells; in a significant fraction of cases it is associated with another concurrent hematological neoplasm. Molecular analysis of KIT mutations and other associated genetic alterations suggest a common origin in the stem cell compartment. Mast cell infiltration patterns in bone marrow biopsy may be subtle in cases associated with t (8;21) AML. Here we report three cases of clonally related SM-AHN, two cases with SM-CMML and one case with SM- t (8;21) AML. We describe in detail the bone marrow infiltration pattern at diagnosis and during the course of treatment with allogeneic stem cell transplant and novel TK inhibitors, showing the unique dynamics of mast cell clearance after therapy.

Immunohistochemical Staining to Identify Concomitant Systemic Mastocytosis in Acute Myeloid Leukemia with RUNX1::RUNX1T1

Systemic mastocytosis with associated hematological neoplasm (SM-AHN) poses diagnostic challenges because of the coexistence of atypical mast cell proliferation and hematological neoplasms. We assessed the presence of SM-AHN in patients with acute myeloid leukemia (AML) with RUNX1::RUNX1T1 from 2014 to 2020. Bone marrow (BM) samples were evaluated for mast cell aggregates using CD117 and CD25 immunohistochemical (IHC) staining. The KIT D816V variant burden at diagnosis and post induction was assessed using droplet digital PCR. Among 23 patients diagnosed as having AML with RUNX1::RUNX1T1, four (17.4%) were also diagnosed as having SM-AHN. No significant differences in clinical characteristics or overall survival (P=0.565) were observed between patients with or without SM-AHN, except for the presence of KIT variants (P=0.040). After induction therapy, IHC staining revealed the presence of mast cell aggregates in the BM, and the KIT D816V variant burden decreased with decreasing blast count and was similar in BM aspirates, smear slides, and sections. Concomitant SM-AHN was not infrequent in AML patients with RUNX1::RUNX1T1. This study showed the importance of CD117 and CD25 IHC staining after induction chemotherapy for SM-AHN screening, especially in patients with KIT variants.

Comprehensive Analysis of Acquired Genetic Variants and Their Prognostic Impact in Systemic Mastocytosis

Systemic mastocytosis (SM) is a rare clonal haematopoietic stem cell disease in which activating KIT mutations (most commonly KIT D816V) are present in virtually every (>90%) adult patient at similar frequencies among non-advanced and advanced forms of SM. The KIT D816V mutation is considered the most common pathogenic driver of SM. Acquisition of this mutation early during haematopoiesis may cause multilineage involvement of haematopoiesis by KIT D816V, which has been associated with higher tumour burden and additional mutations in other genes, leading to an increased rate of transformation to advanced SM. Thus, among other mutations, alterations in around 30 genes that are also frequently mutated in other myeloid neoplasms have been reported in SM cases. From these genes, 12 (i.e., ASXL1, CBL, DNMT3A, EZH2, JAK2, KRAS, NRAS, SF3B1, RUNX1, SF3B1, SRSF2, TET2) have been recurrently reported to be mutated in SM. Because of all the above, assessment of multilineage involvement of haematopoiesis by the KIT D816V mutation, in the setting of multi-mutated haematopoiesis as revealed by a limited panel of genes (i.e., ASXL1, CBL, DNMT3A, EZH2, NRAS, RUNX1 and SRSF2) and associated with a poorer patient outcome, has become of great help to identify SM patients at higher risk of disease progression and/or poor survival who could benefit from closer follow-up and eventually also early cytoreductive treatment.

Mastocytosis

OBJECTIVES

The 2019 Workshop of the Society for Hematopathology/European Association for Haematopathology received and reviewed cases covering the spectrum of mastocytosis and related diseases, including morphologic mimics, focusing on recent updates and relevant findings for pathologists.

METHODS

The workshop panel reviewed 99 cases of cutaneous and systemic mastocytosis (SM) and SM and associated hematologic neoplasms (SM-AHN).

RESULTS

Despite a common theme of KIT mutation (particularly D816V), mastocytosis is a heterogeneous neoplasm with a wide variety of presentations. This spectrum, including rare subtypes and extramedullary organ involvement, is discussed and illustrated by representative cases.

CONCLUSIONS

In the age of targeted treatment aimed at KIT, the accurate diagnosis and classification of mastocytosis has major implications for therapy and further interventions. Understanding the clinical, pathologic, and genetic findings of mastocytosis is crucial for selecting the proper tests to perform and subsequent arrival at a correct diagnosis in this rare disease.

Morphological characteristics, cytogenetic profile, and outcome of RUNX1-RUNX1T1-positive acute myeloid leukemia: Experience of an Indian tertiary care center

INTRODUCTION

A prototype of good prognosis, t(8;21)-positive AML, has diverse clinical and genetic features which affect its outcome. This study aimed at evaluating the clinico-pathological spectrum of t(8;21)-positive AML and ascertaining prognostic factors influencing its outcome in the Indian subcontinent.

METHODS

A retrospective analysis of 75 cases of t(8;21)-positive AML diagnosed over a period of six years (2013-2018) was carried out. Detailed clinical and laboratory data of the patients were collected from the electronic medical records and reviewed.

RESULTS

Median age was 19.5 years (range 5-75 years) with a M:F of 1.7. Myeloid sarcoma was observed in 9.3% cases. There were 85% FAB AML-M2, 8% AML-M1, and 7% AML-M4 subtypes. Prominent morphological characteristics included dyspoiesis in maturing myeloid cells (83%), long thin tapered Auer rods (58%), cytoplasmic vacuoles (58%), eosinophilia (50%), and mast cells (22%). Auer rods in maturing granulocytes (4% cases) were highly suggestive of the translocation. Additional cytogenetic abnormalities were present in 53% cases. Seventy-one percent (25/35) achieved CR. The overall survival (OS) was 40%, with a median follow-up of 27 months (range 4-57 months). None of the hematological or cytogenetic factors correlated with OS, except for the presence of myeloid sarcoma which had a trend toward poor survival (P = .07).

CONCLUSION

Outcome of t(8;21) AML is not influenced by any of the clinico-pathological parameters, except for a myeloid sarcoma, which may herald a poor prognosis. Recognition of this distinct subtype of AML would facilitate further molecular screening for risk stratification in resource-constrained settings.

Long-term Remission of Acute Myeloid Leukemia Developed From Systemic Mastocytosis by Conventional Chemotherapy

Systemic mastocytosis (SM) is a disorder characterized by abnormal proliferation of mast cells with KIT mutations, especially in codon 816. The prognosis of patients developing acute myeloid leukemia (AML) from SM is extremely poor, and hematopoietic cell transplantation is recommended. Herein, we describe a case of an 8-year-old female diagnosed with SM developing AML. A KIT M541L variant in SM was identified in leukemic cells, normal hematopoietic cells, and buccal mucosal cells, suggesting a germline polymorphism. The patient has remained in complete remission for 39 months after completion of chemotherapy. SM developing AML without a KIT D816 mutation may be not necessarily associated with a poor prognosis.

KIT D816 mutated/CBF-negative acute myeloid leukemia: a poor-risk subtype associated with systemic mastocytosis

KIT D816 mutations (KIT D816mut) are strongly associated with systemic mastocytosis (SM) but are also detectable in acute myeloid leukemia (AML), where they represent an adverse prognostic factor in combination with core binding factor (CBF) fusion genes. Here, we evaluated the clinical and molecular features of KIT D816mut/CBF-negative (CBFneg) AML, a previously uncharacterized combination. All KIT D816mut/CBFneg cases (n = 40) had histologically proven SM with associated AML (SM-AML). Molecular analyses revealed at least one additional somatic mutation (median, n = 3) beside KIT D816 (e.g., SRSF2, 38%; ASXL1, 31%; RUNX1, 34%) in 32/32 (100%) patients. Secondary AML evolved in 29/40 (73%) patients from SM ± associated myeloid neoplasm. Longitudinal molecular and cytogenetic analyses revealed the acquisition of new mutations and/or karyotype evolution in 15/16 (94%) patients at the time of SM-AML. Median overall survival (OS) was 5.4 months. A screen of two independent AML databases (AMLdatabases) revealed remarkable similarities between KIT D816mut/CBFneg SM-AML and KIT D816mut/CBFneg AMLdatabases (n = 69) with regard to KIT D816mut variant allele frequency, mutation profile, aberrant karyotype, and OS suggesting underlying SM in a significant proportion of AMLdatabases patients. Bone marrow histology and reclassification as SM-AML has important clinical implications regarding prognosis and potential inclusion of KIT inhibitors in treatment concepts.

Acute myeloid leukemia with t(8;21)(q22;q22.1)/RUNX1-RUNX1T1 and KIT Exon 8 mutation is associated with characteristic mastocytosis and dismal outcomes

KIT mutations are observed in about 20-40% of acute myeloid leukemia with t(8;21)(q22;q22.1)/RUNX1-RUNX1T1 [abbreviated AML t(8;21) here] with mutations involving exon 17 being the most common. Despite high frequencies of KIT mutations in both AML t(8;21) and systemic mastocytosis (SM), AML t(8;21) associated with SM is uncommon, and restricted to KIT exon 17 mutated cases. In this study, we report two cases of AML t(8;21) associated SM that KIT mutation occurred in exon 8 (T417_D419delinsY). In both patients, the bone marrow displayed increased round/ovoid mast cells with bilobated nuclei and absence of CD2 and CD25 expression. RUNX1/RUNX1T1 fusion was shown in both myeloblasts and mast cells by FISH. Patient #1 was refractory to induction chemotherapy and died at day 50; patient #2 had residual AML, marked SM, and persistent RUNX1/RUNX1T1 fusion after induction therapy.

Acute Myeloid Leukemia with Occult Systemic Mastocytosis or Atypical Mast Cells Post-induction

Systemic mastocytosis (SM) is a state of disease that is related to the clonal, neoplastic proliferation of mast cells. Patients who present with SM-Acute Myeloid Leukemia (AML) often have the worst outcome. We present a case of an 18-year-old female who was diagnosed with AML (FLT3 (Fms like tyrosine kinase 3) and PML-RARA (promyelocytic leukemia-retinoic acid receptor alpha) translocation-negative) and after initial treatment with a standard induction regimen of cytarabine and daunorubicin (3+7 regimen), her bone marrow showed blast cells less than 5% and dense aggregates/sheets of atypical/immature mast cells with immunohistochemical stain CD117+ve and toluidine blue positive in mast cell aggregates. Mastocytosis is a clonal neoplastic proliferation of mast cells that accumulate in one or more organ system. Therefore, it is essential to diagnose systemic mastocytosis, particularly in patients of hematological neoplasms.

Mastocytosis: from a Molecular Point of View

Mast cells (MCs) are physiologically activated by binding of stem cell factor (SCF) to the extracellular domains of the Kit receptor. This binding increases the proliferation and prolongs the survival of normal mature MCs, as well as intensifies the release of mediators. In mastocytosis, somatic mutations of the coding Kit gene cause autocrine dysregulation and lead to constitutive KIT activation even in the absence of its ligand SCF. Clinical symptoms are caused by MC-mediator release and/or infiltration of MCs into tissues. Aberrant KIT activation may result in increased production of MCs in the skin and extracutaneous organs. Depending on the affected organ(s), the disease can be divided into cutaneous mastocytosis (CM), systemic mastocytosis (SM), and localized MC tumors. The updated classification of WHO discriminates between several distinct subvariants of CM and SM. While the prognosis in CM and indolent SM (ISM) is excellent with (almost) normal life expectancy, the prognosis in aggressive SM (ASM) and MC leukemia (MCL) is dismal. The symptoms may comprise urticaria, angioedema, flush, pruritus, abdominal pain, diarrhea, hypotension, syncope, and musculoskeletal pain and are the results of MC infiltration and mediator release into target organs, i.e., the skin, gastrointestinal tract, liver, spleen, lymph nodes, and bone marrow. Mastocytosis differs from a lot of other hematological disorders because its pathology is not only based on the lack of normal function of a specific pathway or of a specific cell type but additionally is a proliferative disease. Currently available treatments of mastocytosis include symptomatic, antimediator and cytoreductive targeted therapies.

Acute Myeloid Leukemia With Inv(16)(p13q22) Associated With Hidden Systemic Mastocytosis: Case Report and Review of Literature

Systemic mastocytosis (SM) is a condition associated with clonal neoplastic proliferation of mast cells. In up to 40% of systemic mastocytosis cases, an associated clonal hematological disease of non-mast cell lineage, such as acute myeloid leukemia (AML), is diagnosed before, simultaneously with, or after the diagnosis of SM. Herein, we report a case of a 30-year-old man diagnosed with AML with inv(16) (p13;q22) CBFB:MYH11. Associated mastocytosis was not noted at diagnosis and was only detected in the bone marrow at time of remission after successful chemotherapy. The diagnosis of mastocytosis was based on the demonstration of a multifocal dense mast cell infiltrate in the marrow biopsy with aberrant immunophenotype, with coexpression of tryptase, CD117, and CD25. The mast cells showed atypical morphology mostly with irregular nuclear contour, bilobed or multilobed nuclei with cytoplasmic hypogranulation or irregular metachromatic granule distribution, and some cells with eccentric nucleus or spindle shape. Reexamination of the pretherapeutic bone marrow with immunostain for tryptase and CD25 revealed that mastocytosis was present from the start but masked by extensive blast proliferation. This case indicates that mast cell infiltrates are sometimes underappreciated at the original diagnosis of AML with inv(16) and that the concurrent diagnosis of SM with AML requires a high index of suspicion supported with comprehensive morphologic and immunohistochemical evaluation for a neoplastic mast cell proliferation.

Hidden mastocytosis in acute myeloid leukemia with t(8;21)(q22;q22)

OBJECTIVES

To assess the frequency of systemic mastocytosis (SM) in a large series of acute myeloid leukemia (AML) with t(8;21)(q22;q22).

METHODS

We retrospectively characterized 40 bone marrow aspirate smears and biopsy specimens from patients with AML with t(8;21) for the presence of SM. Cases were assessed for mast cell morphology and immunohistochemistry, as well as KIT exon 8 and 17 mutational assessment by reverse transcription polymerase chain reaction.

RESULTS

Four patients met criteria for SM, 1 met criteria for myelomastocytic leukemia, and 8 demonstrated the benign finding of mast cell hyperplasia.

CONCLUSIONS

We recommend examining all cases of AML with t(8;21) for the presence of SM via morphology, immunophenotyping, and KIT mutational analysis studies.

Systemic mastocytosis associated with t(8;21) acute myeloid leukemia in a child: detection of the D816A mutation of KIT

Systemic mastocytosis (SM) associated with t(8;21) acute myeloid leukemia (AML) is very rare, and the D816 mutation of the KIT gene has previously been detected only in adult patients. We herein report the case of a 5-year-old female presenting with AML harboring t(8;21)(q22;q22). Her AML was refractory to chemotherapy, and bone marrow mastocytosis developed simultaneously at the initial diagnosis and during chemotherapy. The D816A mutation of KIT was detected. SM associated with t(8;21) AML, accompanied by a KIT mutation in children may result in a poor prognosis, despite the fact that t(8;21) AML are generally considered to have a favorable risk.

Systemic Mastocytosis With Associated Clonal Hematologic Nonmast Cell Lineage Disease: A Clinicopathologic Review

Systemic mastocytosis (SM) is a heterogeneous disease with 6 subtypes, including systemic mastocytosis with associated clonal hematologic nonmast cell lineage disease (SM-AHNMD). Bone marrow biopsy specimens show multifocal aggregates of mast cells with predominantly spindle-shaped morphology associated with a myeloid or, less frequently, a lymphoproliferative neoplasm defined by World Health Organization criteria. Neoplastic mast cells abnormally express CD2 and/or CD25, which may be detected by flow cytometry or immunohistochemistry. The pathogenesis of SM-AHNMD is not well understood; however, combined KIT tyrosine kinase receptor mutations and additional genetic events in myeloid stem cells may have a pathogenic role. Reactive mast cell hyperplasia, monocytic/histiocytic proliferations, SM without sufficient criteria for a diagnosis of AHNMD, atypical mast cells associated with PDGFRA rearrangements, and other tryptase-positive myeloid proliferations should be excluded. Overall, the prognosis is poor and largely related to the AHNMD. Cytoreductive therapies, splenectomy, allogeneic bone marrow transplant, and tyrosine kinase inhibitors, excluding imatinib, may have potential efficacy in the treatment of these diseases.

Myelomastocytic Leukemia With t(8;21) in a 3-year-old Child

Here we report a 3-year-old boy with myelomastocytic leukemia. The patient presented with fatigue and right eye proptosis. Bone marrow revealed acute myeloid leukemia with t(8;21) and trisomy 8. Induction therapy produced marked reduction in marrow myeloblasts with the emergence of 13% atypical mast cells. These cells were subsequently identified in retrospect in the diagnostic marrow consistent with myelomastocytic leukemia. His clinical course was notable for the difficulty in the eradication of the leukemic process and resembled that of adults with systemic mastocytosis with associated hematologic non-mast cell lineage disease. To the best of our knowledge, this is the youngest individual reported. The implications of mast cell lineage involvement in acute myeloid leukemia are reviewed.

Systemic mastocytosis in a child with t(8;21) acute myeloid leukemia

Mastocytosis is primarily limited to the cutaneous variant in pediatric patients. Systemic mastocytosis (SM) has been associated with t(8;21) acute myeloid leukemia (AML) in adults. We provide the first report of a child with t(8;21) AML, diagnosed with asymptomatic SM following four cycles of chemotherapy. Unlike most adults with SM/AML, she was not found to have a c-KIT (D816V) mutation. SM persisted in the bone marrow after completion of chemotherapy, and her AML relapsed 9 months off-treatment. Although she achieved a second remission, mastocytosis persists in the marrow. Pediatric patients with t(8;21) AML/SM may represent a high-risk group despite favorable cytogenetics.

Acute myeloid leukemia with the t(8;21) translocation: clinical consequences and biological implications

The t(8;21) abnormality occurs in a minority of acute myeloid leukemia (AML) patients. The translocation results in an in-frame fusion of two genes, resulting in a fusion protein of one N-terminal domain from the AML1 gene and four C-terminal domains from the ETO gene. This protein has multiple effects on the regulation of the proliferation, the differentiation, and the viability of leukemic cells. The translocation can be detected as the only genetic abnormality or as part of more complex abnormalities. If t(8;21) is detected in a patient with bone marrow pathology, the diagnosis AML can be made based on this abnormality alone. t(8;21) is usually associated with a good prognosis. Whether the detection of the fusion gene can be used for evaluation of minimal residual disease and risk of leukemia relapse remains to be clarified. To conclude, detection of t(8;21) is essential for optimal handling of these patients as it has both diagnostic, prognostic, and therapeutic implications.