Mast cell sarcoma: clinicopathologic and molecular analysis of 10 new cases and review of literature

Mastocytosis

Mastocytosis is a spectrum of clonal myeloid disorders defined by abnormal growth and accumulation of mast cells in various organ systems. The disease is divided into cutaneous mastocytosis, systemic mastocytosis (SM) and mast cell sarcoma. SM is further categorized into several non-advanced and advanced forms. The prognosis of cutaneous mastocytosis and non-advanced SM is mostly favourable, whereas prognosis and survival in advanced SM and mast cell sarcoma are poor. During the past 15 years, major advances have been made in the diagnosis, prognosis and management of patients with mast cell neoplasms. Management of mastocytosis consists of symptomatic therapy, including anti-mast cell mediator drugs, and cytoreductive agents for patients with advanced disease and selected individuals with non-advanced disease, as well as recognition and prevention of comorbidities such as osteoporosis and anaphylaxis. The preclinical and clinical development of KIT-D816V-targeting drugs, such as midostaurin or avapritinib, mark a milestone in improving management, the quality of life and survival in patients with SM. These agents induce major responses or even remission in people with advanced SM and lead to rapid improvement of mediator-related symptoms and quality of life in symptomatic patients.

Mast cell sarcoma with KIT p.D816V mutation and concurrent systemic mastocytosis

Mast cell sarcoma (MCS) is an extremely rare and aggressive form of mastocytosis characterized by highly atypical mast cells with local invasion, metastatic potential, and poor prognosis. MCS is predominantly a de novo process without recurrent molecular findings or predisposing lesions including various myeloid neoplasms. However, there have been rare case reports of MCS with preceding or concurrent systemic mastocytosis (SM) or cutaneous mastocytosis (CM), which is suggestive of an uncommon progression from SM/CM to MCS. We hereby report a case of MCS in an 84-year-old male with a KIT p.D816V mutation and concurrent SM. KIT p.D816V point mutation is well known as the canonical variant in SM. In our case, MCS with KIT p.D816V mutation is a unique finding in the setting of concurrent SM, highlighting the potential relatedness of these two entities and the progression from SM to MCS, a currently poorly understood phenomenon.

Primary Mast Cell Sarcoma of the Maxillary Sinus and Gingiva Mimicking Malignant Neuroendocrine Tumor: A Case Report

Mast cell sarcoma (MCS) is an extremely rare and aggressive malignancy primarily affecting bones, with limited literature associating it with neuroendocrine marker expression. This report presents a rare case of MCS arising in the maxillary sinus and gingiva. A 74-year-old man presented with a progressively enlarging ulcer on the right-sided upper gingiva. Magnetic resonance imaging revealed a 3.4 cm tumor on the floor of the right maxillary sinus. The patient underwent an inferior maxillectomy and right-sided neck dissection. Microscopically, the tumor consisted of monotonous round cells with oval nuclei, vesicular chromatin, inconspicuous nucleoli, and brisk mitoses. A panel of immunohistochemical stains was initially applied to exclude common sinonasal undifferentiated neoplasms, such as sinonasal undifferentiated carcinoma, melanoma, rhabdomyosarcoma, Ewing sarcoma, and lymphoma. The tumor cells showed patchy staining for INSM1 and synaptophysin, but were negative for AE1/AE3, CAM5.2, p40, chromogranin, S100, HMB45, NKX2.2, desmin, CD45 (LCA), CD3, and CD20, with intact INI1 and BRG1 expression. No specific diagnosis could be rendered based on the staining results, leading to consideration of other rare malignancies. Additional staining revealed positivity for CD117, mast cell tryptase, CD13, CD33, CD43, and CD68, confirming the MCS diagnosis. Molecular testing for KIT mutation was negative. Subsequent bone marrow biopsy demonstrated infiltration of atypical mast cells, which led to a diagnosis of mast cell leukemia. Despite high-dose chemotherapy, the patient died three months after the initial diagnosis. The undifferentiated epithelioid morphology and unusual aberrant neuroendocrine marker expression posed significant diagnostic challenges. The major differential diagnoses were discussed in this report.

Mast Cell Sarcoma Mimicking Lymphoma or Metastatic Disease on 18 F-FDG PET/CT

ABSTRACT

We report an 18 F-FDG PET/CT scan of a 47-year-old man diagnosed with diffuse mast cell sarcoma with lymph node, bone, liver, spleen, and lung involvement. This interesting image should remind colleagues to consider mast cell sarcoma as a rare differential diagnosis in patients with multiple, intensely hypermetabolic lesions in various organs and lymph nodes.

Intracranial invasion of a mast cell tumour in a dog: A case report and review of the literature

An 11-year-old, female-neutered beagle was presented with a growing soft tissue mass arising within the deep tissues of the left cranial cervical region. At presentation, facial asymmetry was evident along with palpable lymphadenomegaly. Magnetic resonance imaging demonstrated a locally invasive cervical mass with intracranial invasion through focal osteolysis of the occipital bone. After antihistamine administration, cytology confirmed mast cell tumour (MCT) with metastasis to local lymph nodes and liver. The owner chose to pursue lomustine and prednisolone, which were dispensed, but, before home administration, prolonged seizures/status epilepticus occurred prompting euthanasia. Postmortem examination confirmed a high-grade MCT associated with, and infiltrating through, muscle, calvarium, dura mata, leptomeninges and the underlying brain. We present the clinical, imaging, and pathological findings of an unprecedented case of extracranial MCT tumour causing osteolysis of an imperforate flat bone (occipital bone) and intracranial invasion.

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.

The international consensus classification of mastocytosis and related entities

Mastocytosis is a neoplasm characterized by a clonal proliferation of mast cells, which accumulate in one or multiple organs, associated with an extremely heterogeneous clinical presentation. The disease can be limited to the skin (cutaneous mastocytosis) that is mostly seen in childhood and usually behaves in a benign fashion. Adult patients most often present with systemic disease with or without skin lesions. This includes indolent forms such as indolent systemic mastocytosis and its subvariant bone marrow mastocytosis, and smoldering systemic mastocytosis as well as aggressive forms including aggressive systemic mastocytosis, systemic mastocytosis with an associated myeloid neoplasm (previously called systemic mastocytosis with an associated hematologic neoplasm), and mast cell leukemia. In addition, mast cell sarcoma is a rare aggressive form of mastocytosis that can present in the skin as well as at extracutaneous sites. This review article focuses on the updates in mastocytosis of the 2022 international consensus classification (ICC).

Standards of Pathology in the Diagnosis of Systemic Mastocytosis: Recommendations of the EU-US Cooperative Group

Pathology plays a central role in the diagnosis of systemic mastocytosis (SM), its delineation from other neoplasms and reactive conditions, and in monitoring of SM under therapy. The morphologic hallmark of SM is the accumulation of spindle-shaped, hypogranulated mast cells (MCs) in bone marrow (BM) and other extracutaneous tissues. Four of the 5 World Health Organization-defined diagnostic criteria (ie, compact MC aggregates [=major criterion]; atypical MC morphology; activating KIT point mutations; aberrant expression of CD25 and/or CD2 and/or CD30 in MCs [=minor criteria]) can be addressed by the pathologist. The final classification of SM variants as either BM mastocytosis, indolent SM, smoldering SM, aggressive SM (ASM), SM with an associated hematologic neoplasm (SM-AHN), or MC leukemia (MCL) has important prognostic significance and requires the integration of certain morphological, clinical, radiological, and biochemical data, referred to as B- and C-findings. Substantial diagnostic challenges may be posed to the pathologist and clinician especially in the so-called advanced SM variants, that is, ASM, MCL, and SM-AHN. In this article, updated recommendations of the EU-US Cooperative Group regarding standards of pathology in the diagnosis of SM, presented during the year 2020 Working Conference held in September in Vienna, are reported.