BCL2 and keratin 5 define the uterine-cervix-isthmus junction, a transition between endocervical and tubal-like epithelium.

A clearcut definition of the transition from the cervix to the lower uterine segment is lacking. We therefore evaluated the location of the anatomic border between the cervix and the uterine corpus. Using both morphometry and immunohistochemisty, we examined the epithelial and stromal cell types in this transition zone. In 26 patients, longitudinal sections from the cervix uteri up to the fundus uteri were paraffin embedded and immunohistochemically stained for BCL2, keratin 5, Ki-67, CD10, and CD34. Examination of the slides resulted in the identification of a junctional zone in the cranial portion of the cervix, which is characterized by a usually abrupt morphologic and immunohistochemical transition from an endocervical-type mucinous epithelium to a ciliated tubal-like epithelium and a slow transition in stromal marker expression patterns. This epithelial transition was characterized by its intense keratin 5 and BCL2 staining with accompanying Ki-67 expression in the tubal-like epithelium, whereas the endocervical epithelium was largely negative for these markers. CD10 expression was usually quite intense directly around endocervical invaginations, but the remaining stroma was negative. Toward the endometrial cavity, expression increased and endometrial stroma displayed full thickness expression for CD10. CD34 showed a reverse pattern to CD10, with moderate expression in the endocervical stroma, which disappeared in the endometrial stoma. The immunohistochemical identification of this transition may allow a more objective determination of the extension of endometrial carcinoma into the cervix in cases that are morphologically problematic. Furthermore, as ciliated tubal-like epithelium is invariably found cranial to the uterine-cervix-isthmus junction, a diagnosis of tubal metaplasia should not be made in this region and tubal-like epithelium is not indicative of a metaplastic process.