S15C2P5-Atypical Histiocytoma



S15C2P5-1: At a lower magnification, and to the left of the centrally located follicle, the infiltrate of S100 protein (+) dendritic histiocytes is prominent in the reticular dermis among collagen bundles. To the right of the follicle, there are scattered positive dendritic cells in a diffuse infiltrate of histiocytes. The histiocytes of the diffuse component are only faintly positive. Dendritic histiocytes of the follicular epithelium serve as a built-in control.

S15C2P5-2: With an immunoreaction for Kp-1, all of the cells of the infiltrates are positive.

S15C2P5-3: An immunoreaction for MAC387, shows scattered positive dendritic cells in the tumor of the dermis, and in the overlying epidermis. The background infiltrate of histiocytes shows faint positivity.

S15C2P5-4: In this field, a focal cluster of histiocytes is immunoreactive for MAC387.

S15C2P5-5: In this area near the epidermis, individual tumor cells, and small clusters of tumor cells, in the dermal component, are faintly immunoreactive for S100 protein. Dendritic histiocytes in the epidermis are reactive.

S15C2P5-6: Tumor cells are strongly and uniformly immunoreactive for factor XIIIa.

S15C2P5-7: In the dermis, in the area at the margin showing a high component of dendritic cells that are reactive for S100 protein, the histiocytes among the collagen bundles are elongated and dendritic; they show uniform nuclear features without the cytologic atypia seen in the more solid portion of the lesion. This lesion is phenotypically diverse; it might be characterized as a polyphenotypic atypical histiocytoma, or atypical juvenile xanthogranuloma.

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