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

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