Expression of α-smooth muscle actin in benign or malignant ovarian tumors

We compared the expression of α-smooth muscle actin (α-SMA) between benign and malignant human ovarian tissues by immunohistochemical staining and Western blot analysis using the monoclonal antibody specific to α-SMA. In normal human ovaries, α-SMA was found in the blood vessel walls, muscle fibers, and stromal cells surrounding the follicles. The main source of α- SMA in the benign ovarian tumors was the blood vessel walls which highly expressed the α-SMA throughout the tumor. In malignant tumor tissues, however, the vessels located in or close to the cluster of cancer cells did not express α-SMA. It corresponded to the results of the Western blot analysis, showing that the amount of α-SMA in malignant ovarian tumor tissues was much smaller than that in benign tumor tissues. Thus, the alteration in α-SMA expression seems to reflect the qualitative difference in vessels between benign and malignant ovarian tissues, and therefore α- SMA is considered to potentially be a histopathologically useful marker for indicating the malignant potential of ovarian tumors.