New Insights into Tumor Heterogeneity: A Case of Solid-Oncocytic Epithelial-Myoepithelial Carcinoma of the Parotid Gland Harboring a HRAS and Heterogeneous Terminating ARID1A Mutation

We report an unusual case of a low-grade EMC with prominent fibrous stroma, an extensive solid-oncocytic differentiation and limited areas of morphological clearly identifiable characteristic biphasic (tubular) differentiation, clear cells and PAS-positive secretions/calcifications. Both areas were investigated by next generation sequencing (Oncomine comprehensive assay) and revealed a typical concordantHRAS p.Q61R mutation. An additional heterogeneousARID1A (p.E672*) terminating mutation with loss of heterozygosity, which could be visualized predominantly in the solid-oncocytic differentiation by immunohistochemical loss of ARID1A protein expression, was found. This is the first case of an EMC of the salivary gland to be described with two separate tumor clones involving concordantHRAS and heterogeneousARID1A mutations. The latter seem to be a “second hit” and was predominantly found in the solid-oncocytic differentiation, suggesting a potential morpho-molecular association.
Source: Head and Neck Pathology - Category: Pathology Source Type: research