Role of fine needle aspiration cytology in the diagnosis of a rare case of a poorly differentiated synovial sarcoma with “Rhabdoid” features, including treatment implications

Abstract

Synovial sarcoma is a high-grade, soft tissue sarcoma that is relatively chemosensitive. Its exact diagnosis is crucial, including differentiation from its closest diagnostic mimic, ie, Ewing sarcoma, in view of different treatment options, including chemotherapy regimens, for both these tumors. A 15-year-old girl presented with a recurrent soft tissue mass in her right popliteal region, which was diagnosed as Ewing sarcoma, based on positive immunoexpression of MIC2/CD99, Fli1 and negative expression of LCA and desmin. During her metastatic "work-up", a popliteal lymph node was identified, which was aspirated and examined. Fine needle aspiration cytology smears showed singly scattered and loose, cohesive clusters of cells containing round to polygonal, to short spindle-shaped nuclei with prominent nuclei, and moderate to abundant cytoplasm, including several "rhabdoid" cells. These features prompted a review of the biopsy of the recurrent tumor, and additional immunohistochemical stains, which revealed positive co-expression of pan cytokeratin (AE1/AE3), epithelial membrane antigen (EMA), along with a characteristic variable staining pattern of INI11/SMARCB1. Subsequently, by fluorescent in situ hybridization (FISH) technique, performed on the paraffin section of the recurrent tumor, 100% tumor nuclei displayed SS18 rearrangement, while none of the tumor cells displayed EWSR1 rearrangement. Diagnosis of poorly differentiated SS with "rhabdoid" features was confirmed. This constitutes as the first case, describing cytopathologic features of a poorly differentiated SS with "rhabdoid" features, initially misdiagnosed as a Ewing sarcoma, on biopsy and confirmed as SS by FISH technique. The diagnostic and treatment implications in this case are discussed herewith. Diagn. Cytopathol. 2017;45:662-667. © 2017 Wiley Periodicals, Inc.

Diagnosing synovial sarcoma by fine‐needle aspiration cytology and molecular techniques

“…Cytologically, SS may pose as challenging to differentiate from other mesenchymal or spindle cell tumours, such as malignant peripheral nerve sheath tumour (MPNST), solitary fibrous tumour (SFT), leiomyosarcomas or spindle cell carcinomas. In addition, poorly differentiated SS may be difficult to differentiate from Ewing sarcoma or rhabdomyosarcoma for example . Given its rarity, there are a limited number of studies performed regarding the cytological features of SS, with a majority of these composed of case reports.…”

“…Poorly differentiated SS did not present with distinct cytomorphological features as compared to monophasic or biphasic SS. In contrast, previous studies reported that poorly differentiated SS were occasionally found to have a predominantly round‐cell morphology, Ewing‐like or rhabdoid features . Currently, the method of treatment do not differ between subtypes of SS, and the distinction of the poorly differentiated subtype is more valuable for differential diagnostic considerations.…”

“…The presence of a biphasic pattern have been associated in some studies with slightly more favourable outcome . The third subtype, poorly differentiated SS, is seen as a form of tumour progression and is associated with more aggressive tumour behaviour and worse prognosis …”

A BAFfling liver aspirate: Metastatic high grade SMARCA4 deficient undifferentiated gastroesophageal junction carcinoma masquerading as a hematolymphoid malignancy

“…It can be differentiated from other cells with eccentric nuclei, like signet ring cells and plasmacytoid cells, by the presence of a dense rounded cytoplasmic inclusion pushing the nucleus to the side. Rhabdoid cells are, however, not specific for tumors characterized by abnormalities in SWI/SNF complex genes like SMARCB1 ‐ and SMARCA4 ‐deficient tumors and synovial sarcomas, but are also seen in malignant melanoma, neuroendocrine tumors, thyroid, renal, and other carcinomas. The cytologic differential diagnosis of BAF‐deficient tumors varies somewhat based on the age of the patient and site aspirated; in a liver aspirate it includes all malignant neoplasms with small to medium‐sized cells with a dispersed cell pattern.…”

Spectrum of Synovial Sarcoma-clinicopathological and Immunohistochemical Correlation

“…Other also shows similar differentiation. [14] Calcifying variant of SS was described only in the present study. Calcifying SS was not described in other studies.…”