Novel fusion KTN1-PRKD1 in cribriform adenocarcinoma of salivary glands located in the parotid gland: Case report including cytologic findings

Background: Cribriform adenocarcinoma of salivary glands (CASG) is a rare, predominantly minor salivary gland tumor first described in 1999. Because the tumor shares morphologic and molecular features with polymorphous adenocarcinoma (PAC), in 2017, the World Health Organization (WHO) included CASG within the spectrum of PAC. Almost 75% of CASG harbor molecular alterations in the PRKD (Protein kinase D) gene family, and some cases show ARID1A (AT-rich interaction domain 1A)-PRKD1 or DDX3X (DEAD-Box Helicase 3 X-Linked)-PRKD1 fusions. Case presentation: A 39-year-old man presented with headache and painless right cheek mass of two years duration. Imaging showed a well-circumscribed, lobulated 1.7-centimeter mass located in the superficial lobe of the right parotid gland. Fine needle aspiration (FNA) of the mass revealed a “salivary gland neoplasm of uncertain malignant potential” (SUMP). Histopathology and immunohistochemical features of the resected tumor showed a primary salivary gland neoplasm with perineural invasion suggestive of cribriform adenocarcinoma of the salivary glands (CASG). Whole exome sequencing (WES) and transcriptome sequencing (RNAseq) of the tumor revealed a novel, intrachromosomal gene fusion: KTN1 (Kinectin1)-PRKD1. Sanger sequencing and Florescent insitu hybridization (FISH) break apart probe results subsequently confirmed the presence of the fusion. The patient recovered from surgery without complications. Conclusion: We report a novel fusion KTN1-PRKD1 in Cribriform Adenocarcinoma of the Salivary Glands located in the parotid gland. Importantly, this KTN1 fusion partner may account for other reports of intrachromosomal fusions in CASG in which the PRKD1 gene partner was not identified.