Neutron Therapy, Prognostic Factors and Dedifferentiation of Adenoid Cystic Carcinomas (ACC) of Salivary Glands

Purpose: Analysis of the efficacy of fast neutron radiotherapy in the treatment of adenoid cystic carcinomas (ACC) of the salivary glands, identification of prognostic variables and dedifferentiation after radiotherapy. Patients and Methods: Histological slides of primary and recurrent lesions of 71 patients were reviewed to confirm the diagnosis and to analyse subtypes. Median follow-up was 52 months. Local control rate and overall survival were analysed in multivariate analysis. Complications are also described. Results: Primary vs. recurrent therapy (p=0.001), margin-status (p=0.01) and subtype (p=0.019) influenced overall survival. Primary vs. recurrent therapy (p=0.001), margin-status (p=0.018) and T-stage (p=0.043) influenced local control rate. Dedifferentiation was seen in only 1/17 cases. Conclusion: The calculated prognostic factors illustrate the importance of a radical primary therapy. Histological subtype is a significant additional factor for overall survival and, in case of dedifferentiation, it is a strong predictor of a detrimental outcome. Malignancies of salivary glands are relatively rare. They account for 0.5-3% of all head and neck tumours, of which 35-55% are histological adenoid cystic carcinomas (ACC)