February 2022 – Bone and Soft Tissue Pathology

Epithelioid sarcomas may mimic granulomatous inflammatory processes.

Epithelioid sarcomas may mimic granulomatous inflammatory processes, in part due to an interstitial growth pattern of tumor cells that often show limited cytologic atypia, and thus may be prone to misinterpretation as histiocytes. Additionally, there may be necrosis similar to what may be seen in infectious processes. Epithelioid sarcomas show a predilection for lymph node metastases (not bone metastases). The majority (approximately 95%) of epithelioid sarcomas harbor genetic deletions of SMARCB1, and loss of INI1 expression in tumor cell nuclei is often used as a surrogate marker for this event. By contrast, SMARCA4 gene deletions are seen in fewer than 5% of epithelioid sarcomas, and loss of BRG1 nuclear expression can be used as a surrogate. Finally, CD34 expression occurs in approximately 50% of epithelioid sarcomas. ERG expression can also be seen in up to 40% of cases. Expression of these markers may lead to a misinterpretation as angiosarcoma, particularly when combined with a pseudovascular morphologic pattern. However, CD31 (a relatively specific vascular marker) is consistently negative in epithelioid sarcomas.

References

1. Oda, Y., Nielsen, T.O., Dal Chin, P., et al. World Health Organization Classification of Tumours, Bone and Soft Tissue Tumours, 5^th ed. 2020. International Agency for Research on Cancer. 33, 127.