Abstract. 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

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) arising from the minor and major salivary glands (1). ACC usually grow slowly, but have a high incidence (51%) of local recurrence after surgery (2) and metastases may occur even many years after treatment. Histologically, tumours show infiltrative and invasive growth patterns and frequently perineural spread, often leading to underestimation of the true extent. Compared to other cancers of the head and neck, ACC are more difficult to clear surgically, frequently resulting in positive margins (3). Neck metastases range from 15 to 20% (1, 4). Histologically three different subtypes exist: tubular, cribriform and solid, and prognosis is related to the subtype independent of primary tumour localisation (2, 5, 6). Prognosis is worst in the solid subtype (7, 8), while best in the tubular. Surgery is the treatment of choice for patients with operable tumours. Indications for postoperative radiotherapy include involved surgical margins, perineural invasion, neck node metastases, recurrent tumours and advanced T-stage (9, 10). Battermann et al. (11) popularized fast neutron beam therapy as treatment for ACC. Neutron beam therapy improves disease-free and overall survival in patients with unresectable tumours and those with recurrent neoplasm according to some publications (12, 13), but only local control in others (14, 15). In this retrospective study, we reviewed the results of neutron radiotherapy of 71 patients with ACC of the salivary glands who were treated with curative or palliative intent at the Department of Radiation Oncology, University of Hamburg, Germany. Histological slides of the primary tumour and the slides in case of recurrence were reviewed in the Department of Oralpathology (Prof. Donath) and the histological subtypes analysed. We looked for prognostic factors for overall survival and local control rate. In case of recurrence after radiotherapy, we were looking for tumour dedifferentiation as a progression of ACC from highgrade to low-grade histology, indicated by changing of subtype from tubular or cribriform to solid subtype. Patients and Methods Patient characteristics. Between 1985 and 1996, 71 patients with ACC of the salivary glands received neutron radiotherapy at the University of Hamburg, Germany. The median age at therapy was 55 years (range: 26 84 years). The tumours of the minor salivary glands were classified according to the topographic localisation 1321 Correspondence to: Dr. Sophie Brackrock, Department of Radiation Oncology, Friedrich Ebert Hospital, Friesenstr. 11, 24534 Neumünster, Germany. Tel: 00 49 432149 49 90, Fax: 0049 – 4321 – 494999, e-mail: [email protected]