What is an epithelioid sarcoma?

What is an epithelioid sarcoma? Epithelioid sarcoma is an exceedingly rare high-grade malignancy of unknown lineage with no normal cellular counterpart. The tumor has an indolent course but a high potential to metastasize. It is remarkable for being a difficult diagnosis, both clinically and histologically, resulting in a high frequency of initial misdiagnosis. Diagnosis is reached on average 8 years after initial clinical presentation.