Tumors of the uterine isthmus: clinicopathologic features and immunohistochemical characterization of p53 expression and hormone receptors.

Five (3%) of 161 endometrial cancers treated surgically between 1988 and 1992 were classified as primary isthmic tumors, and their clinicopathologic features, p53 expression, and hormone receptor status were evaluated. Three were endometrioid adenocarcinomas with squamous differentiation, one was a mixed serous and clear cell carcinoma, and one was a malignant müllerian mixed tumor; all five were high grade, invaded the entire thickness of the myometrium, and exhibited lymphatic space invasion. Four of the five patients had extrauterine metastases identified at the time of hysterectomy. All five patients died due to progressive disease with the survival time ranging from 1 to 23 months. Abnormal p53 gene expression was identified immunohistochemically in three of the five isthmic tumors. Weak positivity for estrogen and progesterone receptors was demonstrated in one case, with the remaining four being negative. Tumors arising in and confined to the uterine isthmus are unusual and, in our series, were uniformly aggressive with an unfavorable prognosis. The histopathologic features and biologic behavior of the isthmic tumors appeared similar to those of other high-grade endometrial cancers arising in the uterine corpus.