Salivary gland carcinoma in Shanghai (2003–2012): an epidemiological study of incidence, site and pathology

BACKGROUND: Salivary gland carcinoma ranks the sixth in head and neck cancers while it is relatively rare in its incidence. Epidemiological studies have been based mostly on institutional data, leading to selection bias in incidence evaluation. Most population-based cancer registries have grouped cancers of the minor salivary glands with oral cancer instead of with salivary gland carcinoma as a whole, because of the international disease coding. Thus, the incidence of salivary gland carcinoma has not been well assessed. The aim of the study is to evaluate the incidence of both minor and major salivary gland cancers in Shanghai during the years 2003–2012, and to analyse the site and histological distributions. METHODS: Data from the Shanghai Cancer Registry system were extracted for patients diagnosed with malignancies of the major or minor salivary glands for the year 2003 to 2012. Pertinent socio-demographic data were obtained from the Shanghai Municipal Bureau of Public Security. The age-standardized incidence rates were calculated directly according to the world standard population. The change in incidence during the study period was analysed by comparing the rates during the first and next five years. The distributions of anatomic subsites and histology were also analysed. RESULTS: A total of 1831 cases were identified, representing 0.35% of all malignancies during the study period. The median age was 59 and 57 years for men and women, respectively. The age-standardized incidence was 7.99 per 1,000,000 person-year, with a male-to-female ratio of 1.10. There was no significant change in the incidence during the 10-year period. The anatomic distribution confirmed the 4:1:2 rule for the parotid, submandibular, and minor glands. In men, adenocarcinoma not otherwise specified was the most common histological type followed by mucoepidermoid; in women, the mucoepidermoid was the most common histotype, followed by the adenoid cystic. CONCLUSION: Salivary gland carcinoma is relatively rare in incidence. However, the variations in age and sex distribution in sites and histology types suggest differences in aetiology which warrants further investigation.