Low-grade Papillary Nasopharyngeal Adenocarcinoma: A Clinicopathologic Series of 35 Cases.

Low-grade nasopharyngeal papillary adenocarcinoma (LGNPPA) is a rare neoplasm originating from the surface mucosal epithelium in the nasopharynx. To clarify its clinicopathologic, immunohistochemical, and molecular features, we retrospectively enrolled 35 patients diagnosed with LGNPPA between May 2016 and March 2024. Our cohort consisted of 14 male and 21 female patients aged 11 to 71 years (median: 37 y). The most common symptoms were rhinorrhea and nasal obstruction. Most tumors originated from the roof of the nasopharynx and were clinically staged as T1N0M0. None of the patients had a history of thyroid tumors. Microscopically, most of the LGNPPA were composed of irregular papillary structures covered with single-layer columnar or cuboidal epithelium. Eighteen cases (18/35, 51.4%) showed squamous epithelium coverage, and 9 cases (9/35, 25.7%) showed the characteristic transformation of squamous epithelium into neoplasm. Squamous differentiation and a significant spindle cell component were noted in 9 cases (9/35, 25.7%) and 26 cases (26/35, 74.3%), respectively. All cases were positive for thyroid transcription factor-1 protein, CK7, EMA, and Galectin-3 but negative for thyroglobulin, PAX8, and Napsin A. Ki-67 labeling was low and ranged from 2% to 5%. The Epstein-Barr virus or human papilloma virus infection and BRAF V600E mutation were not detected in any of the cases. All patients underwent endoscopic surgical resection, and 4 patients received radiotherapy followed by endoscopic surgery. Complete follow-up data were available for 33 patients. All patients had no recurrent or metastatic disease in the last follow-up (3 to 88 mo). A definitive diagnosis depends on histopathology and immunohistochemistry studies. The optimal treatment for patients with LGNPPA is total excision. Given the extremely indolent biological behavior of LGNPPA, it may be more appropriate to classify it as a primary papillary epithelial tumor rather than an adenocarcinoma of the nasopharynx.