Purpose: To examine the efficacy of fast neutron radiotherapy for the treatment of locally advanced and/or recurrent adenoid cystic carcinoma of the head and neck and to identify prognostic variables associated with local-regional control and survival.
Methods and materials: One hundred fifty-nine patients with nonmetastatic, previously unirradiated, locally advanced, and/or recurrent adenoid cystic carcinoma (ACC) of the head and neck region were treated with fast neutron radiotherapy during the years 1985-1997. One hundred fifty-one patients had either unresectable disease, or gross residual disease (GRD) after an attempted surgical extirpation. Eight patients had microscopic residual disease and were analyzed separately. Sixty-two percent of patients had tumors arising in minor salivary glands, 29% in major salivary glands, and 9% in other sites such as the lacrimal glands, tracheal-bronchial tree, etc. Fifty-five percent of patients were treated for postsurgical recurrent disease and 13% of patients had lymph node involvement at the time of treatment. The median duration of follow-up was 32 months (range 3-142 months). Actuarial curves for survival, cause-specific survival, local-regional control, and the development of distant metastases are presented for times out to 11 years.
Results: The 5-year actuarial local-regional tumor control rate for the 151 patients with GRD was 57%; the 5-year actuarial overall survival rate was 72%; and the 5-year actuarial cause-specific survival rate was 77%. Variables associated with decreased local-regional control in the patients with GRD as determined by multivariate analysis included base of skull involvement (p < 0.01) and biopsy only versus an attempted surgical resection prior to treatment (p = 0.03). Patients without these negative factors had an actuarial local-regional control rate of 80% at 5 years. Patients with microscopic residual disease (n = 8) had a 5-year actuarial local-regional control rate of 100%. Base of skull involvement (p < 0.001), lymph node metastases at the time of treatment (p < 0.01), biopsy only prior to neutron radiotherapy (p = 0.03), and recurrent tumors (p = 0.04) were found to be associated with a diminished cause-specific survival as ascertained by multivariate analysis. Patients with base of skull involvement and positive lymph nodes at presentation had an increased rate of the development of distant metastases at 5 years, (p < 0.01 and p < 0.001, respectively). No statistical difference in outcome was observed between major and minor salivary gland sites.
Conclusions: Fast neutron radiotherapy is an effective treatment for locally advanced ACC of the head and neck region with acceptable toxicity. Further improvements in local-regional control are not likely to impact survival until more effective systemic agents are developed to prevent and/or treat distant metastatic disease.