Immunohistochemical analysis of phospho-mTOR and phospho-p70S6K in ECD lesions. Two ECD cases located in the skin (A-C) and bone (D-F) where the lesional CD68-KP1–positive histiocytes (B,E) show immunoreaction for phospho-p70S6K (C,F). In panels 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) that also react with an anti–phospho- mTOR antibody (I). Original magnification: A-I, ×20; insets in D-F, ×40. HE, hematoxylin and eosin. See Figure 3 in the article by Gianfreda et al that begins on page 1163.