Fig. 1.

Anaplastic astrocytoma with piloid features (pilocytic astrocytoma with anaplasia) arising in the cerebellum of a 29-year-old NF1-patient. Well-differentiated pilocytic astrocytoma component (top a, b) and sharp interface with an anaplastic component characterized by high cellularity and brisk mitotic activity (bottom a, d). ATRX loss detected by immunohistochemistry in well-differentiated (c) and anaplastic (e) components. Positive cells in the stroma and vessels serve as an important internal control (scale bar representing 100 µm applicable to panel a; scale bar representing 50 µm applicable to panels b–e).