Histopathologic studies of basal cell adenoma of the parotid gland.

Five-hundred-thirty-one cases of primary epithelial tumors of the parotid gland were examined. The incidence of basal cell adenomas was 7.5% (40 cases). The tumors could be classified histologically into these subtypes: basal cell (21/40; 42.5%); tubular, (13/40; 32.5%); trabecular (4/40; 10.0%); and papillary (2/40; 5.0%). The pattern of classic basal cell adenoma predominated in the basal-cell type but was also seen in varying degrees in the latter three types with a reciprocal transition. Accordingly, it could be suggested that tubular, trabecular, and papillary types are variants of basal cell adenoma. The higher incidence of basal cell adenomas in our survey could be accounted for by this categorization. Histologically, basal cell adenomas presented various features; (1) cystic formation (26/40; 65.0%), being most frequently seen in tubular and trabecular types; (2) adenoid cystic pattern (4/40; 10.0%); (3) elastosis in the stromal tissues (2/40; 5.0%). Basal cell adenomas were clinicopathologically compared with 291 cases of pleomorphic adenomas. Basal cell adenomas were seen more often in female patients, (60.0%), as were pleomorphic adenomas (68.4%). They were observed more frequently in patients over 50 years of age and the average was ten years higher than for pleomorphic adenoma. The tumor size tended to be smaller (below 2 cm at the greatest diameter) than pleomorphic adenomas.