Cytomorphological features of adamantinoma-like Ewing's sarcoma in parotid masquerading as sialoblastoma in a paediatric patient

Adamantinoma-like Ewing Sarcoma (ALES) May Harbor FUS Rearrangements : A Potential Diagnostic Pitfall

Adamantinoma-like Ewing sarcoma (ALES) is a rare malignancy currently considered a variant of Ewing sarcoma with most known cases harboring EWSR1 rearrangements. Herein we present a series of 6 cases of EWSR1 -negative ALES. The tumors arose in the sinonasal tract (n=3), major salivary glands (submandibular gland=1; parotid=1), and anterior mediastinum (n=1) in patients ranging from 25 to 79 years of age. Most tumors were basaloid in appearance, growing in large nests separated by interlobular fibrosis without overt squamous pearls. However, 1 case closely resembled a well-differentiated neuroendocrine tumor with uniformly round nuclei, eosinophilic cytoplasm, and trabecular architecture. All cases were diffusely positive for pan-cytokeratin, p40 or p63, and CD99. A subset of cases showed diffuse reactivity for synaptophysin, including 1 sinonasal tumor which also demonstrated sustentacular S100 protein expression. Molecular testing showed FUS rearrangements in all cases. Gene partners included known ETS family members FEV (n=2) and FLI1 (n=1). Our results expand the molecular diagnostic considerations for ALES to include FUS rearrangements. We also show that ALES may harbor FUS :: FLI1 fusion, which has not been previously reported in the Ewing family of tumors. Furthermore, ALES may show unusual histologic and immunophenotypic features that can overlap with olfactory carcinoma including S100-positive sustentacular cells. ALES should be considered in the diagnostic differential of small round cell tumors and tumors with neuroendocrine differentiation with immunohistochemical workup to include p40 and CD99/NKX2.2.

Transcriptomic and immunophenotypic characterization of two cases of adamantinoma-like Ewing sarcoma of the thyroid gland

INTRODUCTION

Adamantinoma-like Ewing sarcoma (ALES) is a rare aggressive malignancy occasionally diagnosed in the thyroid gland. ALES shows basaloid cytomorphology, expresses keratins, p63, p40, frequently CD99, and harbours the t(11;22) EWSR1::FLI1 translocation. There is debate on whether ALES resembles more sarcoma or carcinoma.

METHODS

We performed RNA sequencing from two ALES cases and compared findings with skeletal Ewing's sarcomas and nonneoplastic thyroid tissue. ALES was investigated by in situ hybridization (ISH) for high-risk human papillomavirus (HPV) DNA and immunohistochemistry for the following antigens: keratin 7, keratin 20, keratin 5, keratins (AE1/AE3 and CAM5.2), CD45, CD20, CD5, CD99, chromogranin, synaptophysin, calcitonin, thyroglobulin, PAX8, TTF1, S100, p40, p63, p16, NUT, desmin, ER, FLI1, INI1, and myogenin.

RESULTS

An uncommon EWSR1::FLI transcript with retained EWSR1 exon 8 was detected in both ALES cases. Regulators of EWSR1::FLI1 splicing (HNRNPH1, SUPT6H, SF3B1) necessary for production of a functional fusion oncoprotein, as well as 53 genes (including TNNT1, NKX2.2) activated downstream to the EWSR1::FLI1 cascade, were overexpressed. Eighty-six genes were uniquely overexpressed in ALES, most of which were related to squamous differentiation. Immunohistochemically, ALES strongly expressed keratins 5, AE1/AE3 and CAM5.2, p63, p40, p16, and focally CD99. INI1 was retained. The remaining immunostains and HPV DNA ISH were negative.

CONCLUSION

Comparative transcriptomic profiling reveals overlapping features of ALES with skeletal Ewing's sarcoma and an epithelial carcinoma, as evidenced by immunohistochemical expression of keratin 5, p63, p40, CD99, the transcriptome profile, and detection of EWSR1::FLI1 fusion transcript by RNA sequencing.

Adamantinoma-like Ewing sarcoma of the salivary glands: a case report and systematic literature review

Adamantinoma-like Ewing sarcoma (ALES) of the salivary glands is an exceedingly rare malignancy defined by the t(11,22) EWSR1::FLI1 fusion, with complex epithelial differentiation. To identify features that can allow for better recognition of this disease entity, we reviewed all published reports of molecularly confirmed ALES of the salivary glands and explored epidemiological, clinical, radiological, pathological, and therapeutic characteristics of a population of 21 patients including a single newly reported patient from our group. We searched the English-language literature indexed in PubMed, Medline, Scopus, and Web of Science using the keyword 'Adamantinoma-like Ewing sarcoma' published up to June 2022. The median age at diagnosis was 46 years, and a slight female sex predilection was observed. Most tumors originated in the parotid gland (86%) and presented as a painless palpable mass with a median diameter of 3.6 cm. Metastatic dissemination was reported only in one patient (5%), and after a median follow-up of 13 months the 1-year overall survival rate was 92%. Salivary gland ALES were frequently misdiagnosed at presentation (62% of cases) and were pathologically characterized by the presence of highly monomorphic small round blue cells with infiltrative pattern and positive immunostaining for CD99 and high- and low-molecular weight cytokeratins. Epidemiological and clinical features of salivary gland ALES raise questions on the incorporation of this malignancy in the Ewing sarcoma family tumor group.

Fine-needle aspiration cytology of adamantinoma-like Ewing sarcoma: An unusual parotid tumor

Adamantinoma-like Ewing sarcoma (ALES) is a histological subtype of Ewing sarcoma that demonstrates the morphological and immunohistochemical features of the latter, harbors the EWSR1::FLI1 gene fusion, and additionally demonstrates complex epithelial differentiation on morphology and immunohistochemistry. Accurate preoperative diagnosis has potential to inform management and improve patient outcome. Cytomorphology of ALES is not well documented, with available reports showing a spectrum of features. An aspirate from a 30-year-old male with a swelling in right parotid region, interpreted elsewhere as acinic cell carcinoma (ACC), was submitted to us for review. Smears showed dispersed cells and loosely cohesive clusters with scant cytoplasm and large nuclei with focal nuclear molding, prompting a diagnosis of malignant neoplasm, possibly neuroendocrine carcinoma. Cytoplasmic vacuoles and tigroid background were present focally, the former of which had possibly led to interpretation as ACC. No material was available for ancillary tests. Parotidectomy revealed features of ALES. The cytological features of ALES in the parotid overlap with several basaloid and round blue cell neoplasms that are more common at this site. ALES should be considered in all salivary gland aspirates with isomorphic small round or basaloid cells, with or without the presence of squamous differentiation. Rosettes, cytoplasmic vacuoles, and a tigroid background are subtle morphological clues to the diagnosis, which if suspected on cytomorphology, can be confirmed using ancillary techniques.

Adamantinoma-like Variant of Ewing Sarcoma in the Metatarsal Bone After Chemotherapy: Report of a Case Successfully Treated with Pedicled Osteocutaneous Fibular Transfer

Adamantinoma-like Ewing sarcoma is a rare variant of Ewing sarcoma with histologic and immunohistochemical evidence of squamous differentiation. This variant most commonly occurs in the head and neck region with a few cases reported in the long bones of the limbs. It may be associated with poorer clinical outcome and could pose a diagnostic challenge, particularly if it occurs in older patients or as a metastatic lesion. We present a case of Ewing sarcoma in the metatarsal of an 11-year-old boy that manifested adamantinoma-like morphology after neoadjuvant chemotherapy. Chemotherapy has been reported to induce neuronal maturation and rhabdoid morphology in cases of Ewing sarcoma, but no reports of treatment-induced squamous differentiation with P40/P63 expression have been demonstrated. This is also the first documented case treated with a pedicled osteocutaneous fibular transfer in a metatarsal malignancy, which is usually treated by either ray or below-knee amputation.