Salivary gland tumours: an epidemiological review of non-neoplastic and neoplastic pathology

Salivary gland tumours (SGT) demonstrate geographical variation. The primary objective of this study was to determine the types, frequency, distribution, and demographics of non-neoplastic and neoplastic salivary gland pathology at Waikato Hospital, New Zealand (NZ) over a 10-year period. Following this we conducted a 10-year retrospective review of SGT epidemiology from international literature. In total 825 patients were identified, 31% (256/825) with non-neoplastic salivary gland pathology, 34% (284/825) with benign neoplastic pathology, 14% (118/825) with primary malignant lesions, 18% (146/825) with metastatic SGTs, and 3% (21/825) with lymphoma. Patients had a mean (range) age of 58 (3-102) years, were predominantly male (58%, 476/825), and NZ European (65%, 536/825). Tumours were most prevalent in the parotid gland (85%, 484/569), of which 44% (211/484) were malignant. Pleomorphic adenoma was the most common benign (71%, 203/284) and overall (36%, 203/569) tumour, while mucoepidermoid carcinoma (25%, 29/118) and squamous cell carcinoma (SCC) (73%, 106/146) were the most common primary malignant and metastatic SGTs, respectively. Our literature review identified 18 studies consisting of 33,933 patients, of whom 71% (24,013/33,933) had benign SGTs. Pleomorphic adenoma (68%, 16404/24013) and mucoepidermoid carcinoma (29%, 2826/9621) were the most common benign and malignant SGTs, respectively. Low numbers of non-neoplastic and metastatic SGTs were reported in the literature. This research provides a greater understanding of differences in their global distribution. Consistent with previous literature, pleomorphic adenoma and mucoepidermoid carcinoma were the most common benign and malignant SGTs. In NZ, we found high rates of malignant SCC to the parotid gland, consistent with the epidemiology of non-melanoma skin cancer in the country.