Diffuse p16 positivity is nearly always encountered in endocervical adenocarcinoma in situ (AIS), (given its association with high-risk HPV) and is of great diagnostic utility in the differential diagnosis with benign glandular lesions such as microglandular hyperplasia (MGH), tuboendometrial metaplasia (TEM), and endometriosis [5,22,23]. The gene discussed is CDKN2A; the disease is endometriosis.