Subglottic Laryngeal Salivary Gland Intraductal Papillary Mucinous Neoplasm with GNAS Mutation: A Case Report and Review of the Literature.

INTRODUCTION: Salivary gland intraductal papillary mucinous neoplasm (SG IPMN) is a recently described entity arising predominately from intraoral minor salivary glands, characterised by a low-grade papillary cystic proliferation of mucinous columnar cells, so-named due to its resemblance to the pancreatic duct counterpart [1]. It is currently mentioned in the World Health Organization (WHO) Classification of Tumours (5th edition) salivary gland tumours introduction as a lesion with low-grade mucinous morphology that shares frequent AKT1 mutations with mucinous adenocarcinoma, hence it is thought to represent a low-grade salivary gland mucinous adenocarcinoma and is currently subsumed into this entity [1-3]. However, the classification of the neoplasm remains a controversial issue, with the WHO noting that it is still not established whether SG IPMN should be classified separately or within the mucinous adenocarcinoma spectrum as a potential precursor [2]. METHODS: We describe an unusual case of a minor salivary gland papillary mucinous neoplasm presenting in a novel location (subglottic larynx) with a novel mutational driver for this entity (GNAS R844H mutation), and briefly review the literature surrounding SG IPMN, its classification and related tumours.