Two cases of adenocarcinoma in situ arising in lobular endocervical glandular hyperplasia indicating localization of mucin on the cluster surface as an early cytological finding of malignant transformation

Lobular endocervical glandular hyperplasia (LEGH) is an endocervical glandular hyperplastic lesion containing pyloric gland‐like mucin, and has recently been recognized as a precursor lesion of malignant glandular lesions of the endocervix. The pyloric gland‐like mucin contained in LEGH and gastric‐type adenocarcinoma is observed as golden‐yellowish by Papanicolaou staining. However, to our knowledge, the chronological course of the endocervical cytology of LEGH, eventually resulting in malignancy, has never been demonstrated to date. Here, we report two cases of gastric‐type adenocarcinoma in situ (AIS) arising in LEGH, together with an analysis of their cytological course. In both cases, localization of mucin on the surface of glandular cell clusters was observed prior to nuclear atypia in endocervical cytology. In addition, the diagnosis of gastric‐type AIS arising in LEGH was confirmed by pathological diagnosis of hysterectomy specimens in both cases. Histologically, all glandular cells of the LEGH without nuclear atypia contained a large amount of PAS‐positive mucin. On the other hand, in atypical glandular cells, localization of the mucin on the luminal surface was observed, although mucin was abundant throughout the cytoplasm in some areas. Our cases show the course of acquirement of cytological atypia of LEGH, and indicate the significance of localization of mucin on the surface of glandular cell clusters as an early finding of the malignant transformation of LEGH in endocervical cytology. Our results indicate that the distribution of mucin in glandular cells should be analyzed together with nuclear atypia in the endocervical cytology of suspected cases of LEGH.