Systemic Mastocytosis

Authors

Cyrus Oster, MD (Fellow) and Mark Ewalt, MD (Attending)

Subject: Hematopathology
Clinical History

A 73-year-old female with a history of uterine adenocarcinoma treated with surgery and XRT in 2007 presents with slowly progressive macrocytic anemia and thrombocytopenia. Serum B12 and iron levels at the time of consultation were normal. A bone marrow biopsy was subsequently performed.

Figures
Dyserythropoiesis, bone marrow aspirate smear, Cedars-Sinai

Figure 1. Dyserythropoiesis is observed in the bone marrow aspirate smear.

bone marrow, core biopsy, hypercellular marrow, erythroid hyperplasia

Figure 2. Review of this bone marrow core biopsy demonstrates a hypercellular marrow with erythroid hyperplasia.

multiple mall clusters, atypical mast cells, spindled morphology

Figure 3. There are multiple small clusters of atypical mast cells composed of >15 cells and many show spindled morphology.

Immunhistochemistry
atypical mast cells,positive,mast cell tryptase

Figure 4. The atypical mast cells are positive for mast cell tryptase.

atypical mast cells,aberrant expression,CD2

Figure 5. The atypical mast cells demonstrate aberrant expression of CD2.

cells, aberrant expression, CD25

Figure 6. The atypical mast cells also demonstrate aberrant expression of CD25.

Prussian blue, stain, bone marrow, smear, Cedars-Sinai

Figure 7. A Prussian blue stain performed on a bone marrow aspirate smear shows adequate storage iron and numerous ring sideroblasts. Ring sideroblasts are increased accounting for >15% of erythroid precursors.

Additional Studies

A myeloid malignancies panel was performed by next generation sequencing (NGS) which demonstrated an SF3B1 K700E mutation with a variant allele fraction of 31.3%.

Diagnosis

Systemic mastocytosis with associated clonal hematological non-mast cell lineage disease (SM-AHNMD)

Discussion

Mastocytosis is a neoplastic clonal proliferation of mast cells which can occur in one or more organ systems. A diagnosis of systemic mastocytosis is rendered when the major criterion and one minor criterion or at least three minor criteria are observed as defined by the WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues (2016). The major criterion for diagnosis is the presence of clusters of atypical mast cells with at least 15 mast cells forming aggregates. Minor criteria include greater than 25% of mast cells having spindle-shaped or otherwise abnormal morphology, greater than 25% of mast cells being immature or atypical, detection of KIT mutation, aberrant express of CD2 and/or CD25 in addition to normal mast cell marker expression and serum tryptase above 20 ng/mL in the absence of a clonal myeloid disorder. The atypical mast cell findings in this case are consistent with a diagnosis of systemic mastocytosis. The diagnosis of systemic mastocytosis with associated clonal hematological non-mast cell lineage disease (SM-AHNMD) is made when a clonal hematological non-mast cell lineage disorder is present that meets WHO criteria for a distinct entity. In this case the presence of anemia, significant dyserythropoiesis and ring sideroblasts seen in greater than 15% of marrow erythroid precursors is consistent with a diagnosis of myelodysplastic syndrome with ring sideroblasts (MDS-RS), formerly refractory anemia with ring sideroblasts (RARS). This was further supported by the SF3B1 mutation detected by NGS. Somatic mutations of SF3B1 are commonly associated MDS-RS and recent studies show that this mutation portends a favorable prognosis regardless of morphological classification.

References
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