Immunohistochemical analysis of skeletal muscle tumors.A: Biopsies from rhabdomyoma and the 3 rhabdomyosarcoma subtypes, alveolar, pleomorphic and embryonal, were analyzed for expression of Dlk1, Pax7 and Myogenin. Dlk1 was strongly expressed by all skeletal muscle tumor types and can thus be considered a solid marker. Expression of Pax7 and Myogenin in all tumors confirmed the skeletal muscle origin. Scalebar representative for all images: 50 µm. B: Dlk1 expression was detected specifically in cells co-expressing either Pax7 or Myogenin, shown as double staining. Two examples of rhabdomyosarcomas with these co-expression patterns are shown. Scalebar representative for all images: 50 µm.Delta-like 1 homolog (dlk1): a marker for rhabdomyosarcomas implicated in skeletal muscle regeneration. Jørgensen LH, Sellathurai J, Davis EE, Thedchanamoorthy T, Al-Bader RW, Jensen CH, Schrøder HD - PloS one (2013). Not Altered. CC.