Immunohistochemical analysis of phospho-mTOR and phospho-p70S6K in ECD lesions. (A-C) Two ECD cases located in the skin and (D-F) bone, where the lesional CD68-KP1–positive histiocytes (B,E) show immunoreaction for phospho-p70S6K (C,F). In (D-F), the arrowhead indicates some elongated histiocytes, whose shape results from their encasement by abundant sclerotic fibrous tissue. An additional case of ECD involving the skin (G-I) with CD68-KP1–positive histiocytes (H), which also react with an anti–phospho-mTOR antibody (I) is shown. Original magnification: (A-I), ×20; insets in (D-F), ×40. HE, hematoxylin and eosin.