Adenoid Cystic Carcinoma.

Sinonasal adenoid cystic carcinoma is a rare malignancy characterized by an insidious growth pattern and a tendency for perineural spread along major and minor nerves, resulting in invasion of the skull base and intracranial extension. Therefore, many patients present with advanced disease and involvement of critical structures, making treatment difficult and potentially associated with high morbidity. Surgery represents the mainstay of treatment of the primary tumor. Complete resection of the tumor with negative margins, whenever feasible, is associated with better survival outcomes. However, in the case of extensive involvement of vital structures (e.g., carotid artery, cavernous sinus, optic nerve, Meckel's cave) or when radical surgery could seriously affect the patient's quality of life, a function-preserving subtotal removal of the tumor followed by irradiation can be proposed. The role of surgery is limited to a biopsy in unresectable lesions that are more suitable for non-surgical treatments (e.g., exclusive chemoradiation). Given the difficulty in obtaining negative margins and the propensity for submucosal and perineural spread, adjuvant radiotherapy is strongly recommended. Recently, heavy-particle radiotherapy using protons or carbon ions has emerged as a promising treatment with improved local control. Local failures (60%) and distant metastases (40%) are common and can occur even decades after definitive treatment. The 5-year overall survival ranges from 55 to 70% and it exceeds that of other sinonasal malignancies, but dramatically drops down at 10 years (40%) and further decreases at 20 years (15%). Therefore, a prolonged follow-up of at least 15 years, and possibly lifelong, is mandatory.