Undifferentiated Embryonal Sarcoma of the Liver in Adults

Undifferentiated embryonal sarcoma of the liver (UESL) is an aggressive malignancy that most commonly affects the pediatric age group. This tumor very rarely occurs in adults and, in such instances, can pose a considerable diagnostic challenge for the clinicians, radiologists, and pathologists involved. The clinical presentation is most often non-specific, and the radiology shows a solid and cystic liver mass which has a considerable differential on imaging. Especially in adult patients, UESL is a diagnosis of exclusion meaning that all other diagnostic possibilities must be excluded before the diagnosis of UESL can be confidently made. From a pathology perspective, this means careful examination of the histology along with a comprehensive panel of immunohistochemistry for almost all cases of newly diagnosed UESL. The prognosis of UESL used to be dismal, but with advances in treatment and the introduction of a multimodality approach, there has been considerable progress in improving outcomes and survival for patients with this aggressive tumor. This chapter outlines the clinical, radiological, and pathological features of UESL. An in-depth discussion is undertaken to describe the diagnostic approach and the differential diagnosis for this rare and challenging tumor.