MACROSCOPIC APPEARANCE: A 105x85x80mm oval partly lobulated yellow solid lesion with two thirds smooth surface and one third irregular surface received fresh. The specimen 369g. The specimen is serially sectioned to reveal a tan soft to fleshy cut surface with relatively uniform soft to fleshy cut surface.
MICROSCOPIC DESCRIPTION: The sections show a variably hypercellular spindle cell tumour. Tumour cells have moderately pleomorphic vermiform nuclei with coarse bipolar processes and are dispersed within a fibrous and myxoid stroma. Scattered mitotic figures are identified (6 in 40 HPF). No areas of necrosis are seen. Scattered collections of small lymphocytes are noted. The tumour is partially enclosed within a fibrous capsule of varying thickness. No breach of the capsule is seen.
Immunohistochemistry shows strong staining in tumour cells for S-100 protein and variable moderate staining for neurofilament protein (NFP). The topoisomerase labelling index shows a wide variation but is up to 40% in more hypercellular areas.
FINAL DIAGNOSIS: Peripheral nerve sheath tumour of uncertain malignant potential.