Systemic mastocytosis associated with acute myeloid leukemia: case report and implications for disease pathogenesis

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.

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.

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.

A case of systemic mastocytosis associated with acute myeloid leukemia terminating as aleukemic mast cell leukemia after allogeneic hematopoietic stem cell transplantation

In up to 40% of systemic mastocytosis (SM) cases, an associated clonal hematological non-mast cell lineage disease such as AML is diagnosed before, simultaneously with, or after the diagnosis of SM. A 40-yr-old man was diagnosed with AML with t(8;21)(q22;q22). Mast cells were not noted at diagnosis, but appeared as immature forms at relapse. After allogeneic hematopoietic stem cell transplantation (HSCT), leukemic myeloblasts were not observed; however, neoplastic metachromatic blasts strikingly proliferated during the state of bone marrow aplasia, and finally, aleukemic mast cell leukemia developed. As the disease progressed, we observed serial morphologic changes from immature mast cells with myeloblasts to only metachromatic blasts and atypical mast cells as mast cell leukemia; FISH analysis showed that the neoplastic mast cells originated from the same clone as the leukemic myeloblasts of AML.

Variable presence of KITD816V in clonal haematological non-mast cell lineage diseases associated with systemic mastocytosis (SM-AHNMD)

In a substantial number of patients with systemic mastocytosis (SM), an associated clonal haematological non-mast cell lineage disease (AHNMD) is detectable. Although most of these patients display KIT mutations, especially KIT(D816V), little is known about their exact frequency and their distribution in AHNMD subtypes. We examined 48 patients with SM-AHNMD for the presence of mutant KIT in the SM and AHNMD components of the disease. Mast cells and AHNMD cells were obtained from immunostained bone marrow sections by laser microdissection and examined by melting point analysis of nested-PCR products. KIT(D816V) was found in AHNMD cells in the vast majority of patients with SM-chronic myelomonocytic leukaemia (CMML, 89%). Unexpectedly, KIT(D816V) was far less frequently detectable in AHNMD cells in patients with SM-myeloproliferative neoplasm (MPN, 20%) and SM-acute myeloid leukaemia (AML, 30%). None of the patients with lymphoproliferative AHNMDs displayed KIT codon 816 mutations in AHNMD cells (0/8). In FIP1L1/PDGFRA-positive chronic eosinophilic leukaemia (CEL), neither the SM nor the CEL component of the disease exhibited the KIT mutation. Our findings demonstrate that KIT codon 816 mutations are variably present in AHNMD cells in patients with SM-AHNMD, depending on the subtype of AHNMD. The high frequency of KIT(D816V) in neoplastic mast cells and leukaemic myelomonocytic cells in SM-CMML may point to a common precursor in these patients, and may have implications for the biology of the disease and the development of KIT-targeting therapies.

Therapy-related myeloid neoplasms

Session 5 of 2007 Workshop of the Society for Hematopathology/European Association for Haematopathology focused on therapy-related myeloid neoplasms. This report discusses the diversity and relevance of clinical, pathologic, and genetic features and provides an update on the pathogenesis of these disorders. We highlight common diagnostic issues such as the differentiation between therapy-related myelodysplastic syndrome and therapy-related acute erythroid leukemia. As similar therapeutic interventions are frequently considered for patients with either of these diagnoses, in the current World Health Organization classification, regardless of morphologic presentation, therapy-related myeloid neoplasms are considered together as a unique clinicopathologic syndrome of therapy-related myelodysplastic syndrome/acute myeloid leukemia. Nevertheless, recognition of the diverse morphologic features is crucial as bone marrow morphologic examination remains the first and important step of patient evaluation. We also present examples of therapy-related acute myeloid leukemias with recurrent cytogenetic abnormalities. In these cases, the precise classification is clinically important because it is associated with distinct clinical outcome.

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

Although KIT mutations are present in 20–25% of cases of t(8;21)(q22;q22) acute myeloid leukemia (AML), concurrent development of systemic mastocytosis (SM) is exceedingly rare. We examined the clinicopathologic features of SM associated with t(8;21)(q22;q22) AML in ten patients (six from our institutions and four from published literature) with t(8;21) AML and SM. In the majority of these cases, a definitive diagnosis of SM was made after chemotherapy, when the mast cell infiltrates were prominent. Deletion 9q was an additional cytogenetic abnormality in four cases. Four of the ten patients failed to achieve remission after standard chemotherapy and seven of the ten patients have died of AML. In the two patients who achieved durable remission after allogeneic hematopoietic stem cell transplant, recipient-derived neoplastic bone marrow mast cells persisted despite leukemic remission. SM associated with t(8;21) AML carries a dismal prognosis; therefore, detection of concurrent SM at diagnosis of t(8;21) AML has important prognostic implications.

Systemic mastocytosis with acute myelomonocytic leukemia: a case report

Bone marrow mastocytosis may be associated with many clonal non mast cell hematological neoplasms and its association with acute myeloid leukemia especially with t (8; 21) has been described. We describe an interesting case of coexistence of systemic mastocytosis with acute myelomonocytic leukemia in a young child. Diagnosis of acute myelomonocytic leukemia was based on bone marrow aspirate findings coupled with cytochemistry. Systemic mastocytosis was diagnosed on the basis of bone marrow biopsy findings showing blasts as well as multifocal dense mast cell infiltrates with spindling and atypical morphology which was confirmed on toluidine blue staining.

The identification and characterisation of novel KIT transcripts in aggressive mast cell malignancies and normal CD34+ cells

KIT mutations have been identified in several malignancies, including acute myeloid leukemia (AML) and systemic mastocytosis (SM). Mast cell leukemia (MCL) is the most aggressive mast cell neoplasm, but has not been well studied due to its rarity. We identified novel KIT transcripts in two patients with MCL and two patients with SM with an associated hematological disorder, but not from two patients with SM. Similar novel KIT transcripts were also observed in normal CD34+ cells from bone marrow and umbilical cord blood, suggesting that altered KIT isoforms may be specific to the blast stage of hematopoietic precursors. The novel KIT proteins lack several domains including the ATP binding site, and one was inactive in a functional test for autophosphorylation. Our discovery of novel KIT transcripts underscores the importance of analysing entire protein encoding regions when studying genes of interest.

Recent advances in the understanding of mastocytosis: the role of KIT mutations

Mastocytosis is a heterogeneous disorder characterised by the expansion and accumulation of mast cells in different organs and tissues. Mast cell physiology is closely dependent on activation of the stem cell factor/Kit signalling pathways and accumulating evidences confirm the physiopathological key role of activating KIT mutations (typically D816V) in mastocytosis and their relationship with the clinical manifestations of the disease. This paper reviews the most recent advances in the understanding of the molecular mechanisms associated with KIT mutations in mastocytosis, including recent data about the use of new therapies targeting the Kit molecule and its associated downstream signalling pathways.

Flow Cytometric Analysis of Normal and Neoplastic Mast Cells: Role in Diagnosis and Follow-Up of Mast Cell Disease

Human mast cells (MCs) are directly derived from human pluripotent CD34+ stem and progenitor hematopoietic cells with stem cell factor being a critical growth factor supporting human MC proliferation, differentiation, and survival. Because of the advantages that flow cytometry offers (it allows rapid, objective, and sensitive multiparameter analysis of high numbers of cells from a sample, with information being provided on the basis of a single cell), it has become the method of choice in the past decade for immunophenotypic identification, enumeration, and characterization of human MCs in bone marrow and other tissue specimens.