Aleukemic Mast Cell Leukemia with Abnormal Immunophenotype and C-kit Mutation D816V

Acute aleukemic mast cell leukemia: Report of a case and review of the literature

Mast Cell Leukemia (MCL) is the rarest form of systemic mastocytosis, a rare group of neoplastic disease that result from clonal proliferation of mast cells and their accumulation in one or more organ systems. The diagnosis of MCL is made by meeting the World Health Organization (WHO) 2017 criteria. MCL is further subclassified as leukemic or aleukemic based on presence or absence of circulating mast cells in the peripheral blood and acute versus chronic based on presence or absence of findings indicative of impaired organ function due to mast cell infiltration. A 64-year-old Hispanic male presented with myalgia, diarrhea, urticarial rash, back pain, and fulminant disseminated intravascular coagulation. Bone marrow examination, supplemented by immunohistochemistry results, fulfilled the WHO criteria for the diagnosis of MCL. To the best of our knowledge, this is the first documented case of aleukemic acute MCL in a Hispanic patient.

Pharmacotherapy in Mast Cell Leukemia

INTRODUCTION

Mast cell leukemia (MCL) is one of the most aggressive forms of Systemic Mastocytosis (SM), a complex family of rare diseases, for which standard therapies are very few. MCL represents only <1% cases of SM and this is the reason why there are no specific clinical trials to better explore this disease. As a consequence, MCL is treated and grouped within other forms of SM, being all KIT-driven diseases; however, its KIT dysregulation leads to uncontrolled activation of mast cells (MCs), which correlates with forms of myeloid acute leukemia (AML).

AREAS COVERED

Different therapeutic approaches can be followed in the treatment of MCL. The authors look at both symptomatic therapies along with other approaches including targeted therapy. Further, the authors provide their expert opinion.

EXPERT OPINION

In the scenario of mast cell leukemia treatment, the key approach to achieve clinical results is, more than other similar pathologies, personalizing the therapy. It could be interesting or desirable to introduce for instance KIT mutant forms as minor criteria for the diagnosis of advanced SM, considering the small patient population with MCL and the relatively large panel of activating mutations for KIT and other important proteins involved in MCs' regulation.

Ultrastructural, cytogenetic, and molecular findings in mast cell leukemia: Case report

We report a de novo aleukemic form of MCL with a complex monosomic karyotype with LOH for multiple chromosomes and TP53 mutation. Additionally, whereas D816V KIT was not found, the c-Kit transmembrane domain p.M541L variant was detected which is the most common SNP of KIT gene in humans with controversial pathogenic role. In these cases, it is crucial to perform a rapid broad molecular study for an accurate diagnosis which could help to initiate targeted therapy.

KIT D816V Positive Acute Mast Cell Leukemia Associated with Normal Karyotype Acute Myeloid Leukemia

Introduction

Mast cell (MC) leukemia (MCL) is extremely rare. We present a case of MCL diagnosed concomitantly with acute myeloblastic leukemia (AML).

Case Report

A 41-year-old woman presented with asthenia, anorexia, fever, epigastralgia, and diarrhea. She had a maculopapular skin rash, hepatosplenomegaly, retroperitoneal adenopathies, pancytopenia, 6% blast cells (BC) and 20% MC in the peripheral blood, elevated lactate dehydrogenase, cholestasis, hypoalbuminemia, hypogammaglobulinemia, and increased serum tryptase (184 μg/L). The bone marrow (BM) smears showed 24% myeloblasts, 17% promyelocytes, and 16% abnormal toluidine blue positive MC, and flow cytometry revealed 12% myeloid BC, 34% aberrant promyelocytes, a maturation blockage at the myeloblast/promyelocyte level, and 16% abnormal CD2−CD25+ MC. The BM karyotype was normal, and the KIT D816V mutation was positive in BM cells. The diagnosis of MCL associated with AML was assumed. The patient received corticosteroids, disodium cromoglycate, cladribine, idarubicin and cytosine arabinoside, high-dose cytosine arabinoside, and hematopoietic stem cell transplantation (HSCT). The outcome was favorable, with complete hematological remission two years after diagnosis and one year after HSCT.

Conclusions

This case emphasizes the need of an exhaustive laboratory evaluation for the concomitant diagnosis of MCL and AML, and the therapeutic options.

Masitinib (AB1010), from canine tumor model to human clinical development: where we are?

Masitinib mesylate (AB1010) is a novel potent and selective tyrosine kinase inhibitor, targeting mainly wild-type and mutated c-Kit receptor (c-KitR), Platelet Derived Growth Factor Receptor-alfa/beta (PDGFRa/ß), Lymphocyte-specific kinase (Lck), Lck/Yes-related protein (LYn), Fibroblast Growth Factor Receptor 3 (FGFR3) and Focal Adhesion Kinase (FAK). It is the first anticancer therapy approved in veterinary medicine for the treatment of unresectable canine mast cell tumors (CMCTs), harboring activating c-KitR mutations, at dose of 12.5mg/kg once daily. Considering its anti-proliferative action, principally given by inhibiting the MCs c-KitR anti-angiogenic pathway that leads cancer progression, and its role as chemosensitizer, masitinib is under clinical investigation in several human malignancies (Gastro-Intestinal Stromal Tumors, acute myeloid leukemia, systemic mastocytosis, pancreatic cancer, multiple myeloma, non-small cell lung cancer, melanoma, ovarian and prostate cancer), which are characterized by similar canine c-KIT proto-oncogene mutations. Here, we analyze masitinib structure activity, its pharmacokinetics compared to imatinib, the c-KitR pathway referring to the most frequent c-KIT mutations sensitive or resistant to this novel drug compared to imatinib, and masitinib safety profile. We, also, explore preclinical and clinical (completed and ongoing) trials with the aim to emphasize as this recent anti-angiogenic therapy, at first approved in CMCTs and, currently in development for the treatment of several human neoplasms, could be represent a milestone in translational oncology, in which the murine experimental model of cancer research could be integrated by canine spontaneous tumor model.

Mast cell leukemia

Mast cell leukemia (MCL) is a very rare form of aggressive systemic mastocytosis accounting for < 1% of all mastocytosis. It may appear de novo or secondary to previous mastocytosis and shares more clinicopathologic aspects with systemic mastocytosis than with acute myeloid leukemia. Symptoms of mast cell activation-involvement of the liver, spleen, peritoneum, bones, and marrow-are frequent. Diagnosis is based on the presence of ≥ 20% atypical mast cells in the marrow or ≥ 10% in the blood; however, an aleukemic variant is frequently encountered in which the number of circulating mast cells is < 10%. The common phenotypic features of pathologic mast cells encountered in most forms of mastocytosis are unreliable in MCL. Unexpectedly, non-KIT D816V mutations are frequent and therefore, complete gene sequencing is necessary. Therapy usually fails and the median survival time is < 6 months. The role of combination therapies and bone marrow transplantation needs further investigation.

Systemic Mastocytosis

An unusual disease, mastocytosis challenges the pathologist with a variety of morphologic appearances and heterogeneous clinical presentations ranging from skin manifestations (pruritus, urticaria, dermatographism) to systemic signs and symptoms indicative of mast cell mediator release, including flushing, hypotension, headache, and anaphylaxis among others. In this article, we focus on recognizing the cytology, histopathology, clinical features, and prognostic implications of systemic mastocytosis, a clonal and neoplastic mast cell proliferation infiltrating extracutaneous organ(s) with or without skin involvement. Diagnostic pitfalls are reviewed with ancillary studies to help unmask the mast cell and exclude morphologic mimics.

Mast cell leukemia with rapidly progressing portal hypertension

Reported herein is an autopsy case of mast cell leukemia, a rare form of systemic mastocytosis, complicated with portal hypertension. A 52-year-old woman presented with urticaria-like skin symptoms, anemia, and thrombocytopenia. Atypical mast cells (CD2+, CD25+, CD117+) with toluidine blue metachromasia were found in the peripheral blood and on bone marrow aspiration smears. Chemotherapy with cytosine arabinoside and idarubicin was ineffective and the patient died of multi-organ failure with rapidly progressing hepatosplenomegaly and large-volume ascites 3 months after admission. At autopsy the bone marrow, spleen, liver, and lymph nodes were extensively infiltrated by atypical tumor cells with occasional bi- or multi-lobated nuclei. They were positive for mast cell tryptase and possessed an activating mutation of the c-kitgene (D816V). Ascites (2200 mL) and non-ruptured esophageal varices with submucosal hemorrhage indicated the presence of severe portal hypertension. Although there was no evidence of liver cirrhosis, the hepatic sinusoids were clogged with tumor cells, with a tendency to be more severe in the perivenular areas, and the lumens of central veins were obliterated by tumor cell infiltration. The present case demonstrates that non-cirrhotic portal hypertension due to blocking of sinusoidal and venous flow could be a serious complication in mast cell leukemia.

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.

Mast cell tryptase and microphthalmia transcription factor effectively discriminate cutaneous mast cell disease from myeloid leukemia cutis

BACKGROUND

Cutaneous mast cell disorders are uncommon, but a subset, especially mastocytoma and mast cell leukemia, can histologically mimic myeloid leukemia cutis. Our objective was to employ a panel of cytochemical and immunohistochemical markers to determine which ones would be most useful in separating these two entities.

METHODS

We stained 17 cases of cutaneous mast cell disease and 20 cases of myeloid leukemia cutis with Giemsa, toluidine blue, or pinacyanol erythrosinate (PE), as well as with antibodies against mast cell tryptase, microphthalmia transcription factor (MiTF), CD117 (c-kit), myeloperoxidase, CD43, CD25, CD2, and CD68.

RESULTS

Mast cell tryptase and MiTF emerged as highly sensitive and specific markers for mast cell disease in this context, as both antibodies stained all cases of mast cell diseases but none of myeloid leukemia cutis. Although CD117 stained all cases of mast cell disease, it also stained 2 of 18 cases of myeloid leukemia cutis. PE appeared to be specific for mast cell disease, as 11 of 12 cases stained with this marker, compared with 0 of 18 cases of myeloid leukemia cutis.

CONCLUSIONS

Our results show that mast cell tryptase and MiTF are equally effective in distinguishing mast cell disease from myeloid leukemia cutis.

Pathogenesis, clinical features, and treatment advances in mastocytosis

Systemic mastocytosis (SM) is characterized by the abnormal growth and accumulation of mast cells (MC) in one or more organs. The interaction between the cytokine stem cell factor (SCF) and its cognate receptor, the c-kit receptor tyrosine kinase (KIT), plays a central role in regulating MC growth and differentiation. Whereas germline and somatically acquired activating mutations of KIT have been identified in SM, the issue as to whether individual KIT mutation(s) are necessary and sufficient to cause MC transformation remains unclear based on currently available data. Activating mutations of platelet-derived growth factor receptor-alpha (FIP1 L1-PDGFRA) are identified in a significant number of SM cases that have associated eosinophilia. To date, as with gastrointestinal stromal tumors, activating mutations of KIT and PDGFRA appear to be alternative and mutually exclusive genetic events in SM. The World Health Organization has specified criteria for classification of SM into six major subtypes: cutaneous mastocytosis, indolent systemic mastocytosis (ISM), systemic mastocytosis with an associated clonal hematological non-mast-cell disorder (SM-AHNMD), aggressive systemic mastocytosis (ASM), mast cell leukemia, and mast cell sarcoma. The ability to molecularly classify individual SM cases based on the presence or absence of specific mutations allows for molecularly targeted therapy in a growing number of cases. Imatinib mesylate therapy might result in complete remission of SM cases with wild-type KIT, certain KIT mutations, such as F522C, or the FIP1L1-PDGFRA fusion gene, but not of D816V-KIT-bearing SM. For the latter, interferon-alpha and 2-CdA are potential first- and second-line therapeutic options. Other drugs under investigation include novel tyrosine kinase inhibitors, as well as NF-kappaB inhibitors, which might display greater selectivity towards D816V-KIT as compared to wild type KIT. The pathogenesis of mastocytosis, its major clinical subtypes, and recent treatment advances are discussed in this chapter.

Systemic mastocytosis

Systemic mastocytosis is a fascinating disease with diverse clinical features. There have been numerous advances in understanding the basis of clinical manifestations of this disease and of its molecular pathogenesis in the last several decades. The development of methods to study mast cell biology using cell culture and murine models has proven invaluable in this regard. Clarification of the roles of mast cells in various biological processes has expanded our understanding of their importance in innate immunity, as well as allergy. New diagnostic methods have allowed the design of detailed criteria to assist in distinguishing reactive mast cell hyperplasia from systemic mastocytosis. Variants and subvariants of systemic mastocytosis have been defined to assist in determining prognosis and in management of the disease. Elucidation of the roles of the Kit receptor tyrosine kinase and signal transduction pathway activation has contributed to development of potential targeted therapeutic approaches that may prove useful in the future.

Uncommon phenotypes of acute myelogenous leukemia: basophilic, mast cell, eosinophilic, and myeloid dendritic cell subtypes: a review

The potential of the transformed (leukemic) multipotential hematopoietic cell to differentiate and mature along any myeloid lineage forms the basis for the phenotypic classification of acute and chronic myelogenous leukemia. Although most cases of leukemia can be classified phenotypically by the dominant lineage expressed, the genotype within each phenotype is heterogeneous. Thus, covert genetic factors, cryptic mutations, and/or polymorphisms may interact with the seminal transforming genetic mutations to determine phenotype. The phenotype usually is expressed sufficiently to determine the lineage that is dominant in the leukemic clone by light microscopic examination, by cytochemistry of blood and marrow cells, and by immunophenotyping. The basis for the frequency of the AML phenotypes is unclear, although there is a rough concordance with the frequency of marrow precursor cells of different lineages. The least common AML phenotypes are a reflection of the least common blood or marrow cell lineages: acute basophilic, acute mast cell, acute eosinophilic, and acute myeloid dendritic cell leukemia. We discuss the features of these uncommon phenotypes and review the criteria used for their diagnosis.

Systemic mastocytosis: bone marrow pathology, classification, and current therapies

Mast cell disease (MCD) is characterized by the abnormal growth and accumulation of neoplastic mast cells (MC) in one or more organs. The diagnosis of systemic MCD is most commonly established by a thorough histological and immunohistochemical examination of a bone marrow (BM) trephine specimen. In cases with pathognomonic perivascular and -trabecular aggregates of morphologically atypical MC and significant BM involvement, the diagnosis may be relatively straightforward. In contrast, when a sparse, loose pattern of MC infiltration predominates, or when MCs are obscured by an associated non-MC hematological neoplasm, a high index of suspicion and use of adjunctive tests, including special stains, such as tryptase and CD25, may be necessary to reach a diagnosis. The updated classification for MCD clarifies the clinical and pathological criteria for categorizing patients into relatively discrete subgroups. Some cases, however, such those with Fip1-like-1-platelet-derived growth factor receptor alpha (FIP1L1-PDGFRA)(+) clonal eosinophilia associated with elevated serum tryptase levels, with features that overlap MCD and chronic eosinophilic leukemia, may not be easy to categorize on the basis of this classification. There is no standard therapy for MCD and treatment has to be tailored to the needs of the individual patient. MC-cytoreductive therapies, such as interferon-alpha and chemotherapy, are generally reserved for patients with progressive disease and organopathy. A subset of MCD patients with associated eosinophilia who carry the FIP1L1-PDGFRA oncogene will achieve complete clinical, histological, and molecular remissions with imatinib mesylate therapy, in contrast to those with c-kit D816V mutations. The BM pathology, consensus classification, and current therapies for MCD are further discussed in this article.