Preinvasive lesions of the endometrium.

Endometrial glandular proliferations form a morphological and biologic continuum. The new definition of stromal invasion provides a means of identifying lesions with a relatively high probability of myometrial invasion and malignant behavior. With more standardized terminology and classification, the natural history of preinvasive lesions is better understood. Caution must be exercised because confusion is hard to avoid completely. It is now apparent that the presence of cytological atypia in a preinvasive lesion identifies a lesion at high risk to develop carcinoma. Glandular hyperplasia without cytological atypia identifies a patient likely to have an abnormal endocrine milieu, but it is not a significant preinvasive lesion and has little tendency to develop into one. The presence of cytological atypia provides the basis for selection of therapy.