Primary colonic malignant peripheral nerve sheath tumor with biphasic morphology: A case report

Table 4 Major differential diagnoses considered in the present case and the corresponding pathologic basis

Tumor type	Key morphologic features	Common immunophenotype	Findings in the present case	Diagnostic interpretation
MPNST	Predominantly composed of spindle cells, often with marked atypia, high mitotic activity, and focal necrosis; some cases may show heterologous differentiation or marked morphologic heterogeneity	S-100 often focal or patchy positive; SOX10 may be positive or negative; complete loss of H3K27me3 is common in high-grade tumors	Coexistence of spindle cells and small round cells; S-100 positive, SOX10 negative; complete loss of H3K27me3; Ki-67 approximately 90%	Supported
Gastrointestinal stromal tumor	Spindle cell or epithelioid morphology, often arranged in fascicular, whorled, or palisading patterns	CD117 positive, DOG1 positive, often with CD34 positivity	CD117 negative; DOG1 negative	Excluded
Leiomyosarcoma	Fascicular spindle cell proliferation with eosinophilic cytoplasm and cigar-shaped nuclei	SMA positive, Desmin positive, h-caldesmon positive	SMA negative; dsmin negative	Excluded
Ewing sarcoma/primitive neuroectodermal tumor	Relatively uniform small round blue cells with scant cytoplasm, sometimes with necrosis	FLI1 positive, NKX2.2 positive, EWSR1 rearrangement	NKX2.2 negative; FLI1 negative; and a definite spindle cell component was present	Excluded
Clear cell sarcoma	Clear or eosinophilic tumor cells arranged in nests or fascicles	S-100 positive, HMB45 positive, Melan-A positive	HMB45 negative	Excluded
Melanoma	May show spindle cell or epithelioid morphology with marked atypia, sometimes with melanin pigment	S-100 positive, SOX10 positive, HMB45 positive, Melan-A positive	HMB45 negative; SOX10 negative; no history of melanoma	Excluded
Synovial sarcoma	Monophasic tumors are often composed of relatively uniform spindle cells and may show a vascular-rich background	AE1/AE3 positive, EMA positive, TLE1 positive	AE1/AE3 negative; EMA negative	Excluded

MPNST: Malignant peripheral nerve sheath tumor.