The proteolytic destruction of cyclin B is an important event during cell division. Cyclin B proteolysis is triggered by the anaphase-promoting complex. Therefore, cell cycle dysregulation due to anaphase-promoting complex loss contributes to cell transformation and human carcinogenesis. This study investigates anaphase-promoting complex7 expression in spindle cell breast tumors and also includes a comparison between the proliferation antigen Ki-67 and S-phase fraction. The average values of the anaphase-promoting complex7 and Ki-67 labeling indices increased in order from benign to malignant within the phyllodes tumor group, and the fibroadenoma and juvenile fibroadenoma exhibited lower levels of anaphase-promoting complex7 and Ki-67 expression than did the phyllodes tumor. The frequency of anaphase-promoting complex7-positive stromal cells correlated with Ki-67 expression in phyllodes tumor and in all of the examined breast tumors. The above results indicate that anaphase-promoting complex7 and Ki-67 are closely related to cell proliferation. In addition, phyllodes tumor can be differentiated from juvenile fibroadenoma with increased mitotic figures mimicking phyllodes tumor by anaphase-promoting complex7 and Ki-67 immunochemistry. Because anaphase-promoting complex7 is expressed at higher levels than is Ki-67, it may overcome the limitations of the Ki-67 labeling index with regard to the differentiation of benign phyllodes tumor from fibroadenoma.