Monomorphic adenomas of major salivary glands: a histologic study of 96 tumours.

It has been a little over a decade since monomorphic adenomas were formally recognized as a class of salivary gland tumours separable from the more common pleomorphic adenomas. This short time and a relatively low incidence, estimate at less that 2% of all salivary gland tumours, have not allowed histopathologic review of any sizable number of the tumours. The present study of 102 monomorphic adenomas; 96 in major salivary glands, establishes the histologic heterogeneity of the tumours and permits a classification based on this histologic variation as well as differences in histogenesis. For a number of the tumours, a hamartomatous deviation from stages in the normal organogenesis of salivary glands is strongly suggested. An analogous relationship exists for adenexae of the skin and their tumours. Identification of 12 tumours bearing a striking resemblance to dermal eccrine cylindromas carries the analogy further. Given the acceptance of the classification and time, a correlation of the subtypes of monomorphic adenoma with biological behaviour should follow.