Atypical polypoid
adenomyoma (APA) is a relatively rare benign uterine
tumor, histologically characterized by proliferation of irregular endometrioid glands accompanied by stromal cells of smooth muscle origin. As the epithelial components of APA usually show cytological atypia, a differential diagnosis between this
tumor and
endometrioid carcinoma invading myometrium is often difficult, especially in
curettage material. This distinction is clinically very important to avoid unnecessary
hysterectomy. However, only a few immunohistochemical studies of APA that differentiate it from
malignancy have been published. Therefore, we have investigated the expression of several
antigens in APA and compared them with those present in myoinvasive
carcinoma. Six specimens of APA were studied, along with controls of
endometrioid carcinoma invading myometrium.
Antibodies to p53, Ki-67, CD10, and h-
caldesmon reacted positively using immunohistochemistry. Variable positive expressions of p53 and Ki-67 were observed in both epithelial and stromal components of APA, and in myoinvasive
endometrioid carcinoma. CD10 was negative or partially and weakly positive whereas h-
caldesmon was completely negative in the stromal cells of all 6 specimens of APA. However, in the myometrium in which
endometrioid carcinoma invaded, a fringe-like positive staining pattern was occasionally observed for CD10, whereas a diffuse positive signal was obtained for h-
caldesmon. The results of this study indicate that immunohistochemically, p53, and Ki-67 are not reliable markers but that h-
caldesmon is useful in distinguishing APA from myoinvasive
endometrioid carcinoma. Further, our data suggest that the stromal cells of APA are mainly immature smooth muscle cells, and thus APA may be a mixed
tumor.