Splenic Mastocytosis: Report of Two Cases and Detection of the Transforming SomaticC-KITMutation D816V

Outcome and Prognostic Indicators in Cats Undergoing Splenectomy for Splenic Mast Cell Tumors

This was a multi-institutional retrospective study evaluating the outcome and clinical parameters associated with the postoperative prognosis of 36 cats with splenic mast cell tumors treated with splenectomy. Clinical parameters reviewed included signalment, clinical history, results of staging tests, surgical variables, administration of blood products, presence of metastasis, postoperative complications, administration of chemotherapy postoperatively, chemotherapy protocol, and response to chemotherapy. Overall median survival time was 390 days (range, 2-1737 days). Administration of a blood product (P < .0001), metastasis to a regional lymph node (P = .022), and evidence of either concurrent or historical neoplasia (P = .037) were negatively associated with survival. Response to chemotherapy (P = .0008) was associated with an improved median survival time. Larger-scale prospective studies evaluating different chemotherapy protocols are required to elucidate the discrepancy between lack of survival benefit with administration of chemotherapy and improvement in survival time with positive response to chemotherapy.

KIT mutation analysis in mast cell neoplasms: recommendations of the European Competence Network on Mastocytosis

Although acquired mutations in KIT are commonly detected in various categories of mastocytosis, the methodologies applied to detect and quantify the mutant type and allele burden in various cells and tissues are poorly defined. We here propose a consensus on methodologies used to detect KIT mutations in patients with mastocytosis at diagnosis and during follow-up with sufficient precision and sensitivity in daily practice. In addition, we provide recommendations for sampling and storage of diagnostic material as well as a robust diagnostic algorithm. Using highly sensitive assays, KIT D816V can be detected in peripheral blood leukocytes from most patients with systemic mastocytosis (SM) that is a major step forward in screening and SM diagnosis. In addition, the KIT D816V allele burden can be followed quantitatively during the natural course or during therapy. Our recommendations should greatly facilitate diagnostic and follow-up investigations in SM in daily practice as well as in clinical trials. In addition, the new tools and algorithms proposed should lead to a more effective screen, early diagnosis of SM and help to avoid unnecessary referrals.

Mastocytosis: an unusual clonal disorder of bone marrow-derived hematopoietic progenitor cells

Mastocytosis, an unusual disorder of bone marrow-derived, clonally transformed hematopoietic progenitor cells, exhibits a broad spectrum of clinical and morphologic features ranging from a self-limiting benign disorder (ie, juvenile cutaneous mastocytosis) to highly aggressive neoplasms like mast cell leukemia. Principally, mastocytosis should be divided in 2 main subentities: cutaneous mastocytosis and systemic mastocytosis mainly involving the bone marrow. Mastocytosis is a morphologic diagnosis and should not be diagnosed on the basis of clinical findings alone. Pathologists need to be aware of the disease and its mimickers. Application of the defined diagnostic criteria can confirm or exclude mastocytosis in most cases. Use of antibodies against tryptase, CD117 (KIT), and CD25 is recommended in every suspected case. Because most cases of systemic mastocytosis show a very low degree of infiltration of the bone marrow, antitryptase and anti-CD117 are of major importance for screening and quantification of mast cells, in particular to detect even small compact infiltrates as the only major diagnostic criterion for mastocytosis. Expression of CD25 on mast cells is defined as a minor diagnostic criterion and is usually seen only in mastocytosis but not in reactive states of mast cell hyperplasia.

Mastocytosis in mice expressing human Kit receptor with the activating Asp816Val mutation

Mastocytosis is a rare neoplastic disease characterized by a pathologic accumulation of tissue mast cells (MCs). Mastocytosis is often associated with a somatic point mutation in the Kit protooncogene leading to an Asp/Val substitution at position 816 in the kinase domain of this receptor. The contribution of this mutation to mastocytosis development remains unclear. In addition, the clinical heterogeneity presented by mastocytosis patients carrying the same mutation is unexplained. We report that a disease with striking similarities to human mastocytosis develops spontaneously in transgenic mice expressing the human Asp816Val mutant Kit protooncogene specifically in MCs. This disease is characterized by clinical signs ranging from a localized and indolent MC hyperplasia to an invasive MC tumor. In addition, bone marrow-derived MCs from transgenic animals can be maintained in culture for >24 mo and acquire growth factor independency for proliferation. These results demonstrate a causal link in vivo between the Asp816Val Kit mutation and MC neoplasia and suggest a basis for the clinical heterogeneity of human mastocytosis.