Fig. 2

a Initial tumor (hematoxylin and eosin stain [HE]): moderately increased density of spindle-shaped cells in a fascicular arrangement. b Local recurrence 1 year later (HE): high cellularity, increased mitotic activity, and a high degree of pleomorphism, with the occurrence of bizarre giant cells (inset). c Brain metastasis 9 years later (HE): high cell density, fascicular tissue of slightly pleomorphic, spindle-shaped tumor cells, elevated mitotic activity (inset) and intratumoral necrosis (*) d Immunohistochemical staining of the brain metastasis: positivity for alpha smooth muscle actin (d, upper panel), and sarcomere actin (d, lower panel). Scale bars on a, b, c: 200 µm, on insets: 20 µm, on d: 50 µm