Site and origin of squamous cervical cancer: a histomorphologic study.

Based on extensive histomorphologic study, a concept of cervical carcinogenesis is formulated. Intraepithelial neoplasia arises in well defined and predestined fields that are well demarcated from each other. Different forms of intraepithelial neoplasia coexist and have different topographic distribution. Extension and enlargement of atypical epithelial fields are not brought about by active spread, but by apposition of new fields. Two different pathways exist for the genesis of intraepithelial neoplasia affecting cell types involved in regeneration or transformation. In the majority of cases the precursor lesion is atypical squamous metaplasia in the transformation zone. Less commonly, malignant change occurs in original squamous epithelium, probably via atypical basal hyperplasia. The role of the "last gland" is seen as the anatomic landmark dividing these two areas. So-called minor forms of intraepithelial neoplasia cannot progress and change into carcinoma in situ, as they are differently located.