This 25-year-old patient with a history of Neurofibromatosis type 1(NF1) was found to have a relatively rapidly enlarging 13 cm posterior chest wall mass. The mass was resected.
Based on the clinical history and Figures #1 to #4, what is your diagnosis?
The correct answer is C. MPNST.
Note that the mass appears to extend into the neural foramina (white arrow). The mass showed a multilobulated appearing cut surface with areas of necrosis (black arrows).
The low power image to the left shows a variably cellular lesion. The higher power image to the right shows an entrapped nerve fascicle (large arrow) surrounded by a variably cellular spindle cell neoplasm. The presence of several mature neurons (small arrows) indicates this likely represents the junction with a ganglion.
The higher power shows a cellular spindle cell lesion, arranged in a fascicular pattern. Several mitotic figures (arrows) are present in this field, and the lesion had greater than 10 mitoses per 10 hpf.
The lesional cells showed marked increase in proliferative fraction (left image). There was only patchy weak staining of neoplastic cells for S100 protein (right image).
The clinical and morphologic features are consistent with the diagnosis of malignant peripheral nerve sheath tumor (MPNST) arising in a neurofibroma.
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