DES and rhabdomyosarcoma: Diagnosis confirmation was achieved through immunohistochemical staining. It is important that desmin was being positively expressed by tumor cells because this is a characteristic protein of muscular differentiation, providing evidence that these cells may be characterized as rhabdomyoblasts (Figure 8). This concurs with the diagnosis of rhabdomyosarcoma, a malignant tumor that arises from skeletal muscle precursors.