In most cases of systemic mastocytosis, which is the presence of too many mast cells or mastocytes, there is a very low degree of infiltration of the bone marrow. For this reason, CD117 (shown in the image on right) and mast cell tryptase stains are used to look for and to quantitate mast cells, which would be seen in systemic mastocytosis.
The image below demonstrates mastocytosis in bone marrow shown in an H&E stained section.
