Incidence of Adenoid Cystic Carcinoma in Nova Scotia: 30-Year Population-Based Epidemiologic Study

Introduction: Adenoid cystic carcinoma (ACC) of the head and neck is a rare malignancy of salivary gland origin. Few epidemiologic studies exist assessing the incidence of this tumour. The purpose of the current study was to determine the incidence of ACC of the head and neck in Nova Scotia. Furthermore, we assessed survival outcomes based on presentation sites. Methods: Nova Scotia is an ideal geographic location in which to conduct retrospective case reviews as there are centralized tertiary care centres and minimal population migration. Furthermore, there is an externally and internally validated cancer registry housed in Cancer Care Nova Scotia. Records at Cancer Care Nova Scotia were retrospectively reviewed to identify all reported cases of ACC since 1979. Age-adjusted incidence rates were calculated standardized to the 2001 Canadian population. Survival curves were plotted to allow assessment of overall survival. A log-rank test was used to compare survival curves for age (> 65 and < 65 years old) and presentation sites. Results: One hundred thirty cases of ACC were identified, with 110 presenting as primary tumours in head and neck sites. The mean (standard error) age-adjusted incidence of ACC in Nova Scotia is 4.5 (0.6) cases per 1 000 000. The incidence did not change significantly over time. The most common site of presentation was the minor salivary glands (40%), followed by the submandibular gland (18.2%) and the parotid gland (17.3%). There was no significant difference for overall and disease-free survival between nonsalivary, major salivary, and minor salivary tumours (p = .97). Significant reductions in survival were found for those diagnosed at >65 years of age (p < .014) and those with a sinus presentation (p < .005). Sixteen percent of all head and neck cancer patients experienced a distant metastasis of their primary tumour. Conclusion: ACC of the head and neck is a rare neoplastic condition that most commonly affects the minor and major salivary glands. Although short-term survival is high, nearly half of all patients will develop metastasis or die of complications of local recurrences.