ACC is the most common minor salivary gland neoplasm, followed by AC, malignant mixed tumor, and mucoepidermoid carcinoma. The most common site of origin is the maxillary antrum, followed by the palate and oral cavity. ACC appear identical histologically and behave clinically similarly. Maxillary ACC is a slow growing, locally aggressive tumor with a high propensity for early perineural and hematogenous spread. The local recurrence at the primary site and distant metastasis rates can be higher than 85%. Lymph node involvement is uncommon, and regional failure is rare. Frequently, patients survive for 5-10 years with extensive lung metastasis.

Factors that affect the 10-year survival rate include pathologic evidence of perineural invasion to the skull base and central nervous system (CNS) and the initial treatment modality based on univariate analyses. The characteristic patterns of perineural invasion involve the maxillary, mandibular, and vidian nerves. Then, from the gasserian ganglion, the tumor spreads antegrade towards infratemporal and pterygopalatine fossa or retrograde towards the intracranium. Special attention should be paid to the foramen rotundum, foramen ovale, and vidian canal on imaging studies.

In ACC from other sites, a high histologic tumor grade (eg, solid pattern versus cribriform or tubular pattern) entails a worse prognosis. Such association is not found in maxillary ACC. A possible explanation is that most ACCs of the sinuses are so clinically advanced at presentation that tumor grading is no longer practical.

The treatment of choice is combined en bloc surgical resection and radiotherapy. Unfortunately, advanced tumor stage and complex skull base anatomy preclude en bloc resection with negative surgical margins in many cases.

Studies demonstrate that a carcinoma-free margin is crucial for tumor control and prevention of distant metastases (Konno, 1998). Residue tumor elements have been suggested to cause local recurrence at the skull base, which is the most likely cause of death. Distant metastases are common and usually well tolerated during the early course of the disease. In one study, 58% of patients developed distant metastases within 5 years despite local control at the primary site. The frequent sites of spread are the lungs, bone, liver, brain, and kidneys; this pattern is similar to ACC from other sites of the head and neck. The appearance of distant metastases is not necessarily associated with a rapid fulminating clinical decline.

The disease-specific survival rate range is 75-93% at 5 years. As time progresses, it shrinks to 25% at 15 years. The disease-free survival rate is approximately 22% at 5 years and 13% at 10 years. Contraindications to surgery include superior extension of tumor into dura, posterior extension of tumor beyond the cribriform plate and fovea ethmoidalis, involvement of both optic nerves, and lateral extension into the region of the superior orbital fissure and cavernous sinus.

External beam radiation reduces local recurrence after radical surgery from 100% to 40%. It improves the overall survival rate from 70% to 80% at 5 years. Current research also indicates that neutron beam irradiation may offer a therapeutic advantage over conventional radiotherapy for ACC from other sites. It would be reasonable to use neutron irradiation as the initial adjuvant treatment for ACC from sinonasal tract.