The low-molecular-weight
cytokeratin (CK)
protein CK19 has been shown to have diagnostic use and prognostic significance in some types of human
malignancy, but little is known of its distribution in normal endometrial mucosa or in endometrial
endometrioid adenocarcinoma. However, we had observed that CK19 appeared to selectively label invasive
tumor areas showing microcystic, elongated, and fragmented ("MELF") changes. Therefore, CK19 expression was assessed in 15
hysterectomy specimens showing normal proliferative, secretory, or atrophic endometrial appearances, and in 26
endometrioid adenocarcinoma cases with areas of MELF-type invasion. Normal endometrial glands were usually CK19 positive; however, there was more consistent expression in the functional layer, whereas basal zone epithelium was typically only focally stained. Proliferative epithelium frequently showed basal and apical cytoplasmic accentuation of staining.
Endometrial carcinomas were also CK19 positive, but in most cases there was a distinct
zonal pattern of expression with strong staining only in the central aspects of the larger
tumor glands and weak-to-absent staining in peripheral glandular areas. In contrast, MELF-type
tumor epithelium was consistently and strongly CK19 positive even when the adjacent "conventional"-type
tumor glands were not stained. Intravascular
tumor cells were also highlighted, including 2 cases in which this feature was not identified on
hematoxylin and
eosin stains. Thus CK19 immunohistochemistry was useful in showing the extent of myometrial invasion and subtle foci of lympho-vascular space invasion. Further studies are required to determine the mechanism and
biologic significance of localized alterations in CK19 expression within
endometrial neoplasms.