PMC7443986_01
Epithelioid malignant peripheral nerve sheath tumor (EMPNST). The tumor is seen to be
encapsulated and lobulated (a), and is of variable cellularity (a-c). It is composed of
patternless distributions of slender spindle cells with minimally to mildly atypical
vesicular nuclei and long cytoplasmic processes (a) within delicately collagenous (a) to
focally myxoid stroma (c). There are also highly cellular nodules of plump, polygonal
cells with moderately pleomorphic vesicular nuclei with prominent eosinophilic nucleoli
and irregular chromatin, with moderate to abundant amounts of eosinophilic cytoplasm (b
and c). Atypical mitotic figures can be seen (c). Immunohistochemically, the tumor shows
diffuse, strong positivity for S100 protein (d), which is typical of EMPNST. The tumor
also shows diffuse and strong nuclear expression of SOX10 (e). There is complete loss of
nuclear INI1 expression in the epithelioid cells (f), in contrast to the interspersed
small lymphocytes, which show nuclear retention of INI1.
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The morphological findings in both the biopsy and the resection specimen were similar (Figure 1). Microscopically the tumor was thinly encapsulated and lobulated (Figure 1(a)) and of variable cellularity (Figure 1(b and c)), and was composed of patternless distributions of slender spindle cells with minimally to mildly atypical vesicular nuclei and long cytoplasmic processes within delicately collagenous to focally myxoid stroma (Figure 1(a-c)), intermingled with more cellular nodules of plump, polygonal cells with moderately pleomorphic vesicular nuclei with prominent eosinophilic nucleoli and irregular chromatin, with moderate to abundant amounts of eosinophilic cytoplasm (Figures 1(b and c)). The mitotic index was up to 2 per 10 high power fields (hpf) including markedly abnormal forms (Figure 1(c)). Immunohistochemically, the tumor was diffusely and strongly positive for S100 protein (Figure 1(d)), SOX10 (Figure 1(e)), D2-40, CD56 and glial fibrillary acidic protein in both the epithelioid and spindle cell populations, with focal CD34 expression. There was complete loss of nuclear INI1 expression in the epithelioid cells (Figure 1(f)), although the spindle cells around the nodules of epithelioid cells retained INI1.