Undifferentiated Embryonal Sarcoma of the Liver Presents as a Molecular Mimic of Parasitic Infection.

Medical laboratory tests are becoming more reliable with increased specificity and sensitivity, leading to their use as definitive diagnostic tests for many medical conditions. Enzyme-linked immunosorbent assay (ELISA) tests are convenient, sensitive, and standardly used for rapid detection and quantification of antigens or patient antibodies against specific antigens. However, based upon the specificity and sensitivity of an ELISA test, the results may not be definitive for a specific disease but merely suggestive, due to potential cross-reactivity of antigens and antibodies. Here, we present a case of a 15-year-old male who presented with fever, nausea, and right upper quadrant pain. Computed tomography scan showed an 18-cm liver mass with cystic features. Biopsy results confirmed a diagnosis of undifferentiated embryonal sarcoma of the liver; however, the clinical picture was complicated by positive ELISA results for Echinococcus, Entamoeba histolytica, and histoplasmosis. Due to the absence of travel and positive ELISA result for three different infectious agents, we hypothesize that tumor molecular mimicry might have led to false-positive ELISA results in the absence of infection in this case, demonstrating a limitation of ELISA serology. Critical appraisal of all possible evidence to ensure alignment when assigning the final diagnosis is essential for optimal patient outcomes.