MON-009 Rare Neuroendocrine Tumor of the Left Middle Ear

Abstract Disclosure: A.C. Lopez: None. M. Shahid: None. C.A. Koch: Abbvie. T. Wu: None. Background: Neuroendocrine tumors (NETs) are a heterogeneous group of tumors that can arise from various tissues. Increased awareness of these neoplasms and advanced imaging have led to an uprising detection rate. Case Presentation: A 59 y.o male veteran, with PMH of tinnitus, mixed sensorineural hearing loss bilaterally, TBI from multiple explosions exposure, and chronic headaches who complains of chronic diarrhea, worsening episodic hot flushes with diaphoresis and increasing seizure frequency for the past 2 years. After a MVA, his head CT scan showed a left middle ear mass with mastoid effusion concerning for cholesteatoma. Afterwards, he visited the ED due to bloody otorrhea from the left ear, nausea, vomiting, and headaches. ENT treated him for acute left mastoiditis and otitis media. Symptoms worsened, thus, further workup was performed, and low-grade epithelial neoplasm with neuroendocrine differentiation was diagnosed after a partial removal of the mass in the left middle ear. Immunohistochemical staining revealed tumor cells positive for AE1/AE3, synaptophysin, chromogranin, vimentin, INSM1. The tumor cells were negative for p40, CK7, TTF-1, PAX-8, S-100 and CAIX. Ki-67 index 2%. No mutations were found on Guardant 360 (TMB was 1.0 mut/Mb, stable MSS, PD-L1 CPS <1). FDG-PET scan showed increased metabolic activity at the left middle ear consistent with the known NET and a small hypermetabolic mediastinal lymph node. Postsurgical laboratory testing revealed plasma serotonin <5 ng/ml, urine 5-HIAA 3.6 mg/24h, CgA elevated at 184.5 ng/ml. Normal levels of VIP and somatostatin. Later, he completed left radical mastoidectomy with most symptoms improving, except for ear pain and hearing impairment. CgA has been on monitoring. Discussion: NETs of the ear, specifically middle ear adenomatous neuroendocrine tumors (MEANTs), are rare primary tumors with dual glandular and neuroendocrine differentiation. As illustrated with our case, these tumors are uncommon and present unique challenges in diagnosis and management. Clinical presentation can include hearing loss, aural fullness, tinnitus, and ear pain. Recent research suggests that "middle ear adenomas" are actually well-differentiated epithelial NETs. These tumors show consistent expression of specific markers, highlighting their neuroendocrine nature. While historically considered low-aggression neoplasms, recent studies have challenged this notion, warranting long-term f/u. A systematic review of 198 cases reported a 25% local recurrence rate and 7% metastasis rate over a median follow-up of 5.7 y. Complete surgical resection is considered the gold standard. Lack of reliable prognostic biomarkers and the limited number of large-scale studies, and gaps in current guidelines make management challenging. Rindi G, et al. Overview of the 2022 WHO Classification of Neuroendocrine Neoplasms. Endocr Pathol. 2022 Presentation: Monday, July 14, 2025