Histology of cutaneous mastocytosis

Skin biopsy demonstrating cutaneous mastocytosis. Hematoxylin and eosin stain showing a dense interstitial and perivascular infiltrate of mononuclear cells in the papillary and reticular dermis at low-power (A) and high-power (B) magnification. By immunohistochemistry, the mononuclear cells are positive for c-kit (CD117) (C) and tryptase (D), which is typical of mast cells.