Aims: Malignant rhabdoid tumours (MRTs) and epithelioid sarcomas (ESs) are distinctive malignant neoplasms with characteristic clinicopathological features. However, these two tumour types share some phenotypic features, such as epithelioid/rhabdoid cytology, expression of epithelial markers, andimmunohistochemical loss of INI1. The distinction can be problematic in atypical clinical settings, and ancillary diagnostic tools are needed. The expression of CD34 is widely cited as favouring the diagnosis of ES, but no formal comparative study has been performed in the post-INI1 era. Here, we evaluated theutility of SALL4 for differentiating MRTs from ESs, and compared its performance with that of CD34. Methods and results: Fifteen MRTs and 36 ESs were retrieved. All MRTs and ESs lacked INI1 reactivity, except for one MRT that lacked BRG1. A representative slide from each case was stained using antibodies against SALL4 and CD34. Ten (67%) of the 15 MRTs expressed SALL4. In contrast, only one (3%) of the 36 ESs expressed SALL4. CD34 staining was observed in nine (60%) of the MRTs and 29 (81%) of the ESs. Conclusions: Despite moderate sensitivity, SALL4 expression may aid in distinguishing MRTs from ESs. CD34 was found to have questionable utility in making such distinctions.
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