Fig. 3 | Modern Pathology

Fig. 3

From: Histiocyte-rich rhabdomyoblastic tumor: rhabdomyosarcoma, rhabdomyoma, or rhabdomyoblastic tumor of uncertain malignant potential? A histologically distinctive rhabdomyoblastic tumor in search of a place in the classification of skeletal muscle neoplasms

Fig. 3

Although the tumors tended to grow in a circumscribed manner, as illustrated in Figs. 1 and 2, infiltrative growth into muscle and fat was also present (a). The neoplastic cells were frequently obscured by foamy macrophages and Touton-type giant cells (b). At higher magnification, spindled cells with enlarged, hyperchromatic nuclei were visible. Mitotic activity was extremely low, less than 1/50 HPF in all tumors (c). These spindled cells were highlighted on desmin immunostains (d). The overwhelming majority of the mass represent CD163-positive histiocytes (e). Myogenin (shown) and MyoD1 expression, although present in all cases, was typically very limited in extent (f)

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