ADENOID CYSTIC CARCINOMA OF THE NASOPHARYNX: A RARE CASE AND REVIEW OF PARTICLE THERAPY APPROACHES

Nasopharyngeal adenoid cystic carcinoma (NACC) is an exceptionally rare malignancy, representing <1% of nasopharyngeal tumors. Over the last decade, fewer than 200 cases have been reported worldwide, usually presenting at an advanced stage with perineural invasion and skull base involvement. The role of surgery is often limited, and particle therapy, including intensity-modulated proton therapy (IMPT) and carbon ion radiotherapy (CIRT), has emerged as a promising alternative. We report the case of a 35-year-old male with NACC presenting with nasal obstruction, epistaxis, and cranial nerve involvement. MRI revealed a 45×35×40 mm mass extending to the clivus, cavernous sinus, and parapharyngeal space. Histopathology confirmed adenoid cystic carcinoma (ACC) (cribriform and solid type), with immunohistochemistry positive for CD117 and CK7, focally positive for p63 and smooth muscle actin (SMA), and negative for p40 and Epstein-Barr virus (EBV) (in situ hybridization). The patient underwent IMPT to a total dose of 45 Gy (relative biological effectiveness [RBE]) in 15 fractions, as recommended by a multidisciplinary tumor board. Treatment was well tolerated, with grade 2 mucositis, grade 2 otitis media, and mild xerostomia. However, pulmonary metastases developed within 10 months, and systemic therapy with lenvatinib plus doxorubicin was initiated with limited efficacy. This case illustrates the challenges of managing NACC, emphasizing the role of particle therapy for local control (LC), the importance of multidisciplinary evaluation, and the need for vigilant follow-up given the high risk of distant metastases. Collaborative registries and clinical trials are warranted to optimize treatment strategies for this rare disease.