[INDOLENT SYSTEMIC MASTOCYTOSIS]. Indolent systemic mastocytosis meets the defining criteria for systemic mastocytosis but is also characterized by absence of any associated non-mast cell lineage clonal hematological malignancies, low total mast cell burden, and presence of cutaneous mast cell lesions. This image shows one of several lymphoid aggregates with embedded mast cells (arrows) satisfying the major criterion for systemic mastocytosis, which is defined by the presence of multifocal, dense infiltrate of mast cells (>15 mast cells in aggregates) detected in sections of bone marrow biopsy and/or other extracutaneous organs(s).
/mastocytosis-systemic-indolent-[2-bm101-2].jpeg?Width=600&Height=450&Format=4 "Mastocytosis, systemic, histopathology image")
[INDOLENT SYSTEMIC MASTOCYTOSIS]. Mast cells show abundant purple granules and oval to spindle nuclei in contrast to round and reniform normal nuclei. Systemic mastocytosis should meet at least one of four minor criteria in addition to major criteria. One of the four minor criteria dictates the presence of >25% of the mast cells to be of abnormal morphology either in the bone marrow and/or in any extracutaneous organs.
[INDOLENT SYSTEMIC MASTOCYTOSIS]. Typically abnormal mast cells show spindle morphology and are present in aggregates as shown in this image. Mast cells can be highlighted by special stains including AFB, Toludine blue, and Leder stain. Other minor criteria include presence of point mutation at codon 816 in KIT gene in lesional tissue, abnormal expression of CD2 and/or CD25 by mast cells, and total serum tryptase levels 20 ng/mL in the absence of another clonal myeloid disorder.
/mastocytosis-systemic-indolent-[4-bm101-4].jpeg?Width=600&Height=450&Format=4 "Mastocytosis, systemic, histopathology image")
[INDOLENT SYSTEMIC MASTOCYTOSIS]. This image highlights abundance of mast cells in an aggregate as detected by CD117 immunostaining in a bone marrow core biopsy section. CD117 shows positive staining in all mast cells whether benign or clonal. This stain is much better than any of several histochemical stains used to detect mast cells in bone marrow and any other organ. It can be very useful in the subclassification of various mast cell disorders such as indolent systemic mastocytosis, aggressive systemic mastocytosis, mast cell leukemia and mast cell sarcoma.
[INDOLENT SYSTEMIC MASTOCYTOSIS]. Abnormal mast cells can show long spindled morphology and difficult to identify in routine H&E sections as shown by arrows. However, such spindle cell morphology helps identify presence of abnormal cells in the marrow.
[INDOLENT SYSTEMIC MASTOCYTOSIS]. Singly scattered spindle mast cells can be highlighted by CD117 immunostaining as shown here. Normal mast cells are round and rarely show spindle cell morphology.
[INDOLENT SYSTEMIC MASTOCYTOSIS]. Bone marrow aspirate smear showing a cluster of mast cells in a spicule (some but not all mast cells are numbered). Mast cells are often increased and associated within lymphoid aggregates of lymphoplasmacytic lymphoma and chronic lymphocytic leukemia involving bone marrow. Eosinophils can be increased and associated with mast cells.
[INDOLENT SYSTEMIC MASTOCYTOSIS]. Mast cells with abundant granules are shown containing tryptase, histamine, serotonin, heparin, and other chemical mediators. When released into blood these chemicals may result in headache, flushing, hypotension, syncope, abdominal pain, diarrhea, etc. The symptoms are also related to the organ involvement such as bone marrow in extensive marrow involvement and itching in cutaneous mastocytosis.
[INDOLENT SYSTEMIC MASTOCYTOSIS]. An abnormal mast cell with a long cytoplasmic projection in a bone marrow smear is shown. Normal mast cells do not show such cytoplasmic projections. Fresh bone marrow aspirate should be submitted for KIT (D816V) and FIP1L1/PDGFR mutations for diagnosis and treatment.