[Clinicopathological features of thyroid-like low-grade nasopharyngeal papillary adenocarcinoma]

Objective: To investigate the clinicopathological features, immunophenotype and gene alterations of thyroid-like low-grade nasopharyngeal papillary adenocarcinoma (TL-LGNPPA). Methods: Fifteen case of TL-LGNPPA diagnosed at Zhejiang Cancer Hospital (5 cases) and the First Affiliated Hospital, Zhejiang University School of Medicine (10 cases) from November 2011 to August 2020 were collected. Clinical and pathological examinations, immunohistochemical staining and next-generation sequencing were performed. The clinicopathological and molecular characteristics were summarized, and relevant literature was reviewed. Results: Fifteen patients were identified and included. Their median age was 36 years (range, 20-60 years). The male-female ratio was 1.0∶1.1. The most common symptoms were epistaxis and nasal obstruction. The neoplasms were located on the roof of the nasopharynx or the posterior margin of the nasal septum. The pathological features included complex papillary and glandular structures mainly composed of single or pseudostratified cubic and columnar cells, with mild to moderate cytological atypia. In some cases, spindle cell features, nuclear grooves, ground glass nuclei, squamous metaplasia, or scattered psammoma bodies were identified. In addition, nuclear polar reversal cells, hobnail cells and micropapillary structures were found, but have not been reported in previous literature. Immunohistochemistry showed that the tumor cells were diffusely positive for TTF1, CK7, vimentin and CKpan; focally positive for p40, CK5/6 and p16; and negative for Tg, NapsinA, CK20, CDX2, S-100 and PAX8. The Ki-67 positive rates ranged from 1% to 20% and were≤10% in thirteen cases (13/15). EBER in situ hybridization was negative in all cases. DNA sequencing of 6 specimens was performed and all specimens were found harboring gene mutations (EWSR1, SMAD2, ROS1, JAK3, GRIN2A, ERRCC5, STAT3, and TET2), but no hot spot gene alterations were found. No MSI-H and MMR related gene changes were detected. All tumors showed low tumor mutation burden. All 15 patients underwent endoscopic surgery, and only 1 of them underwent radiotherapy postoperatively. All patients were recurrence free and alive at the end of follow-up periods (range: 23 to 129 months). Conclusions: TL-LGNPPA is a rare indolent tumor of the nasopharynx and exhibits a unique morphology and immunophenotype. Endoscopic resection is an effective treatment for TL-LGNPPA with excellent overall prognosis.