Detection of the KITD816V mutation in myelodysplastic and/or myeloproliferative neoplasms and acute myeloid leukemia with myelodysplasia-related changes predicts concurrent systemic mastocytosis

Utility of KIT Mutations in Myeloid Neoplasms Without Documented Systemic Mastocytosis to Detect Hidden Mast Cells in Bone Marrow

BACKGROUND

KIT p.D816 mutation is strongly associated with systemic mastocytosis (SM). Next-generation sequencing (NGS) is now routinely performed in almost all bone marrow sample and KIT mutations are detected from patients who are not known or suspected to have SM. Therefore, we wanted to assess if KIT mutations in this patient population are associated with unsuspected SM.

METHODS

We searched NGS result in our institution with positive result for KIT mutation from patients with known/suspected myeloid neoplasms. Patients with previously documented history of systemic mastocytosis were excluded. Bone marrow biopsies from patients with KIT mutation were assessed with immunohistochemical stains for CD117 and mast cell tryptase (MST).

RESULTS

Bone marrow biopsies were assessed with immunohistochemical stains for CD117 and mast cell tryptase (n = 49). Most patients had acute myeloid leukemia (AML, n = 38) or chronic myelomonocytic leukemia (CMML, n = 6). Immunohistochemical stains for CD117 and tryptase were performed in all 49 patients. A total of 4 patients (8.2%) showed mast cell nodules where spindled shaped mast cells were present, meeting the WHO criteria for SM. All four patients had KIT p.D816V mutation and had high mutant allelic frequency (∼ 50%) except one patient (1%).

CONCLUSION

We discovered approximately 8% of patients who had myeloid neoplasms with unexpected KIT mutations fulfilled the diagnostic criteria for systemic mastocytosis after additional immunohistochemical studies. Our data support that application of additional immunohistochemical studies is recommended to identify underrecognized SM when KIT mutations are found by molecular assays.

Antibody-Based and Cell Therapies for Advanced Mastocytosis: Established and Novel Concepts

Advanced systemic mastocytosis (SM) is a heterogeneous group of myeloid neoplasms characterized by an uncontrolled expansion of mast cells (MC) in one or more internal organs, SM-induced tissue damage, and poor prognosis. Advanced SM can be categorized into aggressive SM (ASM), MC leukemia (MCL), and SM with an associated hematologic neoplasm (SM-AHN). In a vast majority of all patients, neoplastic cells display a KIT mutation, mostly D816V and rarely other KIT variants. Additional mutations in other target genes, such as SRSF2, ASXL1, or RUNX1, may also be identified, especially when an AHN is present. During the past 10 years, improved treatment approaches have led to a better quality of life and survival in patients with advanced SM. However, despite the availability of novel potent inhibitors of KIT D816V, not all patients enter remission and others relapse, often with a multi-mutated and sometimes KIT D816V-negative disease exhibiting multi-drug resistance. For these patients, (poly)chemotherapy, antibody-based therapies, and allogeneic hematopoietic stem cell transplantation may be viable treatment alternatives. In this article, we discuss treatment options for patients with drug-resistant advanced SM, including novel KIT-targeting drugs, antibody-based drugs, and stem cell-eradicating therapies.

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.

Standards of Genetic Testing in the Diagnosis and Prognostication of Systemic Mastocytosis in 2022: Recommendations of the EU-US Cooperative Group

Mastocytosis comprises rare heterogeneous diseases characterized by an increased accumulation of abnormal mast cells in various organs/tissues. The pathogenesis of mastocytosis is strongly linked to the presence of KIT-activating mutations. In systemic mastocytosis (SM), the most frequent mutation encountered is KIT p.D816V, whose presence constitutes one of the minor diagnostic criteria. Different techniques are used to search and quantify the KIT p.D816V mutant; however, allele-specific quantitative PCR and droplet digital PCR are today the most sensitive. The analysis of the KIT p.D816V allele burden has undeniable interest for diagnostic, prognostic, and therapeutic monitoring. The analysis of non-mast cell hematological compartments in SM is similarly important because KIT p.D816V multilineage involvement is associated with a worse prognosis. In addition, in advanced forms of SM, mutations in genes other than KIT are frequently identified and affect negatively disease outcome and response to therapy. Thus, combined quantitative and sensitive analysis of KIT mutations and next-generation sequencing of other recurrently involved myeloid genes make it possible to better characterize the extent of the affected cellular compartments and additional molecular aberrations, providing a more detailed overview of the complex mutational landscape of SM, in relation with the clinical heterogeneity of the disease. In this article, we report the latest recommendations of the EU-US Cooperative Group presented in September 2020 in Vienna during an international working conference, on the techniques we consider standard to detect and quantify the KIT p.D816V mutant in SM and additional myeloid mutations found in SM subtypes.

Molecular Targeted Therapy and Immunotherapy for Myelodysplastic Syndrome

Myelodysplastic syndrome (MDS) is a heterogeneous, clonal hematological disorder characterized by ineffective hematopoiesis, cytopenia, morphologic dysplasia, and predisposition to acute myeloid leukemia (AML). Stem cell genomic instability, microenvironmental aberrations, and somatic mutations contribute to leukemic transformation. The hypomethylating agents (HMAs), azacitidine and decitabine are the standard of care for patients with higher-risk MDS. Although these agents induce responses in up to 40-60% of patients, primary or secondary drug resistance is relatively common. To improve the treatment outcome, combinational therapies comprising HMA with targeted therapy or immunotherapy are being evaluated and are under continuous development. This review provides a comprehensive update of the molecular pathogenesis and immune-dysregulations involved in MDS, mechanisms of resistance to HMA, and strategies to overcome HMA resistance.

Defining the Criteria for Reflex Testing for BRAF Mutations in Cutaneous Melanoma Patients

Targeted therapy has been developed through an in-depth understanding of molecular pathways involved in the pathogenesis of melanoma. Approximately ~50% of patients with melanoma have tumors that harbor a mutation of the BRAF oncogene. Certain clinical features have been identified in BRAF-mutated melanomas (primary lesions located on the trunk, diagnosed in patients <50, visibly pigmented tumors and, at times, with ulceration or specific dermatoscopic features). While BRAF mutation testing is recommended for stage III-IV melanoma, guidelines differ in recommending mutation testing in stage II melanoma patients. To fully benefit from these treatment options and avoid delays in therapy initiation, advanced melanoma patients harboring a BRAF mutation must be identified accurately and quickly. To achieve this, clear definition and implementation of BRAF reflex testing criteria/methods in melanoma should be established so that patients with advanced melanoma can arrive to their first medical oncology appointment with a known biomarker status. Reflex testing has proven effective for a variety of cancers in selecting therapies and driving other medical decisions. We overview the pathophysiology, clinical presentation of BRAF-mutated melanoma, current guidelines, and present recommendations on BRAF mutation testing. We propose that reflex BRAF testing should be performed for every melanoma patient with stages ≥IIB.

New Insights into the Pathogenesis of Systemic Mastocytosis

Mastocytosis is a type of myeloid neoplasm characterized by the clonal, neoplastic proliferation of morphologically and immunophenotypically abnormal mast cells that infiltrate one or more organ systems. Systemic mastocytosis (SM) is a more aggressive variant of mastocytosis with extracutaneous involvement, which might be associated with multi-organ dysfunction or failure and shortened survival. Over 80% of patients with SM carry the KIT D816V mutation. However, the KIT D816V mutation serves as a weak oncogene and appears to be a late event in the pathogenesis of mastocytosis. The management of SM is highly individualized and was largely palliative for patients without a targeted form of therapy in past decades. Targeted therapy with midostaurin, a multiple kinase inhibitor that inhibits KIT, has demonstrated efficacy in patients with advanced SM. This led to the recent approval of midostaurin by the United States Food and Drug Administration and European Medicines Agency. However, the overall survival of patients treated with midostaurin remains unsatisfactory. The identification of genetic and epigenetic alterations and understanding their interactions and the molecular mechanisms involved in mastocytosis is necessary to develop rationally targeted therapeutic strategies. This review briefly summarizes recent developments in the understanding of SM pathogenesis and potential treatment strategies for patients with SM.

Secondary Resistant Mutations to Small Molecule Inhibitors in Cancer Cells

Secondary resistant mutations in cancer cells arise in response to certain small molecule inhibitors. These mutations inevitably cause recurrence and often progression to a more aggressive form. Resistant mutations may manifest in various forms. For example, some mutations decrease or abrogate the affinity of the drug for the protein. Others restore the function of the enzyme even in the presence of the inhibitor. In some cases, resistance is acquired through activation of a parallel pathway which bypasses the function of the drug targeted pathway. The Catalogue of Somatic Mutations in Cancer (COSMIC) produced a compendium of resistant mutations to small molecule inhibitors reported in the literature. Here, we build on these data and provide a comprehensive review of resistant mutations in cancers. We also discuss mechanistic parallels of resistance.