MIB-1 (Ki-67), p53, estrogen receptor, and progesterone receptor expression in uterine smooth muscle tumors.

The diagnosis of benign, uncertain malignant potential, and malignant uterine smooth muscle tumors depends on mitotic counts, nuclear atypia, and other morphologic features. This study was undertaken to evaluate the utility of selected immunohistochemical markers in differentiating these tumors. Fifteen cases of cellular leiomyoma, 7 cases of smooth muscle tumor of uncertain malignant potential (STUMP), and 12 cases of leiomyosarcoma were immunostained for MIB-1 (Ki-67), p53, estrogen receptor and progesterone receptor (PR) using monoclonal antibodies and the avidin-biotin-peroxidase method. The percentage of cells stained was subjectively assessed to the nearest 5%. One percent was used for rare positive cells. MIB-1 expression of > or =15% was seen in 11 and expression of p53 in > or =15% cells was present in 5 of 12 leiomyosarcomas. MIB-1 and/or p53 expression of >15% was seen in all 12 leiomyosarcomas but in none of the 7 STUMP or 15 cellular leiomyomas. PR was absent in 10 of 12 leiomyosarcomas but present in 7 of 7 STUMP and 14 of 15 cellular leiomyomas. MIB-1 of 5% to 10% was seen in 6 of 7 STUMP but in only 1 of 15 cellular leiomyomas. MIB-1, p53, and PR are useful in differentiating leiomyosarcoma from STUMP and cellular leiomyoma. MIB-1 is useful in distinguishing STUMP from cellular leiomyomas.