Relative frequency of intra-oral minor salivary gland tumors: a study of 380 cases from northern California and comparison to reports from other parts of the world

BACKGROUND: The relative frequency of individual intra-oral minor salivary gland tumors (IMSGT) is not well documented in the literature. The aim of this study was to determine the relative frequency and distribution of IMSGT in an oral pathology biopsy service and to compare the data with similar studies from different parts of the world. METHODS: Files from the Pacific Oral and Maxillofacial Pathology Laboratory of the University of the Pacific, San Francisco, California served as a source of material for this study. Files were systematically searched for all cases of IMSGT during a 20-year period. Tumors were classified according to the 2005 WHO classification of salivary gland tumors. RESULTS: IMSGT were identified in 380 (0.4%) cases of 92 860 accessed. This is the largest series of IMSGT from one source reported in recent years. Of the 380 tumors, 224 (59%) were benign and 156 (41%) were malignant. Of the benign tumors, pleomorphic adenoma (PA) was the most common (39.2%), followed by cystadenoma (6.3%), canalicular adenoma (6.1%), ductal papillomas (4.4%), basal cell adenoma (1.6%), and myoepithelioma (1.3%). Of the malignant tumors, mucoepidermoid carcinoma was the most common (21.8%), followed by polymorphous low-grade adenocarcinoma (7.1%), adenoid cystic carcinoma (6.3%), adenocarcinoma, not otherwise specified (NOS; 2.1%), acinic cell carcinoma (1.6%), clear cell carcinoma, NOS (1.0%), and carcinoma ex PA (0.5%). CONCLUSIONS: Studies related to the relative frequency of individual IMSGTs from different parts of the world are difficult to compare because many studies are outdated, the number of cases is small, the list of tumors is limited, and new entities are not included. To determine the true relative frequency, more studies should be conducted, on a large number of cases from one source, by experienced pathologists in the field of salivary gland tumors.