Adamantinoma-Like Ewing Sarcoma Mimicking Basal Cell Adenocarcinoma of the Parotid Gland: A Case Report and Review of the Literature

Abstract

Adamantinoma-like Ewing sarcoma (AES) is a rare variant of the Ewing family of tumors that resembles classic adamantinoma of bone. AES shows epithelial differentiation and a more complex immunohistochemical expression profile with keratin and basal marker immunoreactivity and can resemble a variety of carcinomas. We report an unusual case of an AES of the parotid gland that mimicked a basal cell adenocarcinoma. Like basal cell adenocarcinoma, this AES showed a nested basaloid proliferation with peripheral palisading in tumor nests with 'basaloid' epithelial differentiation as highlighted by cytokeratin AE1/3 and p40 positivity. However, unlike most basal cell adenocarcinomas, this tumor demonstrated high grade morphology, showed no true ductal or myoepithelial component, and also showed a tendency towards neuroectodermal phenotype with focal rosette formation, CD99 and weak synaptophysin immunoreactivity. EWSR1 and FLI1 fluorescence in situ hybridization confirmed the presence of a translocation supporting the diagnosis of AES. This is the first case of AES presenting as a primary parotid mass highlighting the potential to be mistaken for primary salivary gland carcinomas, which in addition to basal cell adenocarcinoma include other basaloid tumors such as adenoid cystic carcinoma.

Adamantinoma-like Ewing Family Tumors of the Head and Neck

“…Recent studies have demonstrated rare examples exhibiting prominent squamous epithelial differentiation, for which the designation of “adamantinoma-like” EFT or EFT with complex epithelial differentiation has been proposed. (10, 13–18) The degree to which these tumors truly resemble adamantinomas is certainly debatable, but this terminology is historical: the term adamantinoma-like EFT was used since the first few reported cases with this phenotype occurred in the long tubular bones, including tibia and simulated the diagnosis of extragnatic adamantinoma. (10, 13, 14) Only recently similar cases were documented in the head and neck.…”

“…(22) The remaining six cases were diagnosed prospectively in the authors’ respective consultation practices (JAB, RSS, and CRA). One of these cases (case 4) was previously published as a case report,(18) and another case (case 3) was included as part of a series of soft tissue myoepithelial carcinomas due to its EWSR1 gene rearrangement. (23, 24) Each case was examined by routine light microscopy, immunohistochemistry, and fluorescence in situ hybridization (FISH).…”

“…(10–12) While this immunoexpression is usually focal and mainly with low molecular weight cytokeratins, a rare group of EFT known as “adamantinoma-like” EFTs, show complex epithelial differentiation, exhibiting histologic (i.e., squamous pearls, intracellular bridges) and/or immunophenotypic (i.e., diffuse p40 and/or high molecular weight cytokeratin) evidence of squamous differentiation. (10, 13–18) Until recently, adamantinoma-like EFTs had only been encountered in the long bones or surrounding soft tissues. There have now been three separate case reports of adamantinoma-like EFTs in the head and neck: two in the neck soft tissues and one in the parotid gland.…”

“…There have now been three separate case reports of adamantinoma-like EFTs in the head and neck: two in the neck soft tissues and one in the parotid gland. (16–18) In addition, there are two case reports of a tumor described as “carcinoma of the thyroid with Ewing family tumor elements” that likely represents the same entity. (19–21) We present the first case series of adamantinoma-like EFT in the head and neck, including five previously unpublished cases.…”

Head and Neck Round Cell Sarcomas: A Comparative Clinicopathologic Analysis of 2 Molecular Subsets: Ewing and CIC-Rearranged Sarcomas

“…Diagnostic pitfalls stem from the epithelial features identified in these tumors, such as squamoid pearls, intra-epithelial growth, as well as immunoreactivity for epithelial markers. As carcinomas typically outnumber round cell sarcomas in the H&N, the more common entities that adamantinoma-like ES were confused with were: basaloid squamous cell carcinoma, basal cell adenocarcinoma [25], and sinonasal undifferentiated/poorly differentiated carcinoma [19]. The young age at diagnosis and the diffuse/ strong membranous pattern of CD99 reactivity are important clues for a diagnosis of adamantinoma-like ES, which should trigger additional molecular testing.…”