DNA Methylation Profiling Distinguishes Adamantinoma-Like Ewing Sarcoma From Conventional Ewing Sarcoma

Abstract

Adamantinoma-like Ewing sarcoma (ALES) has traditionally been considered a variant of Ewing sarcoma because it generally harbors EWSR1::FLI1 fusions despite showing diffuse positivity for keratins and p40. However, it has become increasingly recognized that different tumors can have identical translocations, including shared fusions between carcinomas and sarcomas, raising questions as to whether ALES might represent a separate entity. Using methylation profiling, we further explored the relationship between Ewing sarcoma and ALES. The archives of multiple institutions were searched for candidate cases of ALES. DNA methylation profiling was performed and results were compared to corresponding data from conventional Ewing sarcoma. Twelve cases of ALES (5 previously reported) were identified in 10 men and 2 women (aged 20-72 years; median age, 41.5 years). Cases included tumors arising in the parotid gland (3), sinonasal cavity (2), submandibular gland (2), thyroid gland (1), neck (1), gingiva (1), hypopharynx (1), and mandible (1). Histologic review consistently showed sheets and nests of basaloid cells within a fibromyxoid or hyalinized stroma. All tumors were positive for at least 1 keratin and CD99 expression, whereas all 10 cases tested were positive for p63 or p40; S100 protein expression was noted in 2 cases. Cases harbored either EWSR1::FLI1 fusions (n = 6), FUS::FLI1 fusions (n = 1), and/or EWSR1 rearrangements (n = 6). Methylation profiling was successful in 11/12 cases evaluated. Unsupervised clustering and dimensionality reduction (Uniform Manifold Approximation and Projection) of DNA methylation data revealed a distinct methylation cluster for all 11 cases, including the tumor with the FUS::FLI1 fusion, which clearly segregated them from the conventional Ewing sarcoma. Follow-up (n = 11, 1-154 months) revealed that 4 patients experienced recurrence and 6 developed metastatic disease. ALES demonstrates a distinct methylation signature from conventional Ewing sarcoma. This finding adds to the distinctive immunoprofile of ALES, suggesting that these 2 tumors should be considered distinct entities rather than histologic extremes of the same disease.

Keywords: EWSR1; Ewing; adamantinoma; sarcoma.

Figure 1.

Histologic sections of ALES showed relatively uniform features including a nested architecture (A), desmoplastic stroma (B), and peripheral palisading (D).

Figure 2.

The cytoplasm of the gingival ALES was more abundant and pale pink (A), while the case which was reviewed post-chemotherapy showed large ganglion-like cells consistent with neuronal maturation (B). Case 4 showed single cell keratinization (C), while case 1 contained deposition of eosinophilic matrix between tumor nests (D).

Figure 3.

Cases of ALES in our cohort had uniform immumoprofiles with consistent expression of high molecular weight cytokeratin (A), p40 (C), and membranous CD99 (D).

Figure 4.

DNA methylation-based clustering of ALES and potential differential diagnoses, after non-linear dimensionality reduction (UMAP).

Figure 5.

Comparison of methylation of the promoter of the DDR2 gene between ALES and conventional Ewing sarcoma.