Adenocarcinoma in situ (AIS) is an intraepithelial precursor lesion containing malignant appearing glandular cells confined to the cervical epithelium. Commonly there is preservation of the normal glandular architecture with an abrupt transition to atypical cells. The atypical cells have enlarged, hyperchromatic, and pseudostratified nuclei, with eosinophilic to mucinous cytoplasm. Mitotic figures and apoptotic bodies can be easily identified. There are many histologic variants including conventional, intestinal, gastric, endometrioid, adenosquamous, and tubal sub-types. Immunohistochemistry shows p16 positivity and a high Ki-67 proliferation index. If left untreated, AIS can progress to invasive adenocarcinoma.
