PECAM1 and endolymphatic sac tumor: Importantly, the observed immunophenotypic heterogeneity—namely, variable GFAP (Patients 2, 4, and 6), CD31/CD34 (Patients 1 and 2), and S-100 (Patients 5 and 7) expression—suggests the existence of distinct clinical genomic ELST subtypes, warranting further investigation.