Fine‐needle aspiration cytology of epithelioid malignant peripheral nerve sheath tumor: A case report and review of the literature

Abstract

The epithelioid variant of malignant peripheral nerve sheath tumor (eMPNST) is an extremely rare soft tissue neoplasm comprising less than 5% of all MPNSTs. It is distinguished cytomorphologically from a conventional MPNST by the presence of polymorphous round epithelioid cells arranged in loose clusters with or without spindled tumor cells. These features pose a diagnostic challenge because the differential diagnosis involves a variety of mesenchymal and non-mesenchymal tumors including epithelioid sarcoma, sclerosing epithelioid fibrosarcoma, malignant rhabdoid tumor, chordoma, metastatic carcinomas, and melanoma. Thus, it may become imperative to perform immunochemical stains on cell blocks of FNA aspirates to arrive at definitive diagnosis. Reports describing the cytologic features of eMPNST are rare. Herein, we report a case of eMPNST with focus on cytomorphologic and cytoimmunochemical features and differential diagnosis.

Metastatic epithelioid malignant peripheral nerve sheath tumor in a known case of neurofibromatosis-1, cytomorphological appearance, and critical analysis of immunohistochemistry

“…About 50%–70% of these tumors show loss of INI-1 on IHC. [ 5 ] However, in this case, INI-1 expression was retained.…”

“…Jiwani et al . [ 5 ] found richly cellular tumor which consists of pleomorphic cells with both spindle and epithelioid morphology showing prominent nucleoli and many mitotic figures with scant pink mesenchymal matrix material in the background. In our case, the aspirate was predominantly hemorrhagic with good cellularity in only one of the smear.…”

“…[ 3 ] Although few case series describing histological features of epithelioid MPNST are reported, cytological characteristics and histocytological correlation are described only in three reported cases. [ 4 5 ] We report a case of epithelioid MPNST in a background of NF-1 with natural course of its progression diagnosed on fine-needle aspiration cytology (FNAC) with histocytological correlation and immunohistochemical characterization.…”

Application of ancillary studies in soft tissue cytology using a pattern‐based approach

“…Epithelioid MPNST is a distinctive clinicopathologic variant, 175 and smears show epithelioid cells with round vesicular nuclei and prominent nucleoli and occasionally vacuolated cytoplasm. 176 In contrast to conventional MPNST, epithelioid MPNST shows diffuse S-100 positivity and frequent loss of INI1 expression. Tumors are negative for HMB-45 and Melan-A, and melanoma should be excluded.…”

“…ALK shows a nuclear membranous staining pattern secondary to ALK ‐ RANBP2 fusion; tumors also show CD30 and desmin positivity. Epithelioid MPNST is a distinctive clinicopathologic variant, and smears show epithelioid cells with round vesicular nuclei and prominent nucleoli and occasionally vacuolated cytoplasm . In contrast to conventional MPNST, epithelioid MPNST shows diffuse S‐100 positivity and frequent loss of INI1 expression.…”