Fig. 4 | Modern Pathology

Fig. 4

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. 4Fig. 4

A diffuse proliferation of foamy histiocytes almost entirely obscures the underlying rhabdomyoblastic tumor (a, b). Most lesions tended to demonstrate a low power histiocytic nature (a) with admixed foamy macrophages (b). The tumor itself was composed of variably pleomorphic spindled cells with abundant, often “glassy”-appearing, eosinophilic cytoplasm. Numerous small histiocytes and other chronic inflammatory cells were also typically present (c). Mitotic activity, although present, was extremely low ( < 1/50 HPF (d). Desmin (e) and CD163 (f) immunostains highlighted the rhabdomyoblastic cells and histiocytes, respectively. Next-generation sequencing showed mutation of the NF1 gene (g)

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