Systemic Mastocytosis is diagnosed by the presence of abnormal collection of mast cells in the bone marrow.  The sine qua non major criteria include multifocal mast cell clusters with atypical morphology in the bone marrow; minor criteria include atypical spindle shaped cells, hypogranulated mast cells, elevated tryptase levels > 20 ng/ml, aberrnat expression of CD 2 and CD25 on mast cells, c-kit codon 816 mutation (rarely variant exon mutations described as in this case on exon 9).  Mast cell leukemia is diagnosed when the peripheral blood atypical mast cells constitute > 10% or bone marrow aspirate shows > 25% mast cells as seen in this case. Less than 10% mast cells in peripheral blood is defined as aleukemic mast cell leukemia.