Caldesmon is a smooth muscle regulatory protein that interacts with actin, myosin, tropomyosin and calmodulin. Caldesmon antibody can label smooth muscle and smooth muscle tumor and it can be used to distinguish between smooth muscle and myofibroblast tumor, or between leiomyoma and endometrial stromal tumor. Caldesmon can be used as a marker for the identification of epithelioid mesothelioma, and has been used to distinguish between epithelioid mesothelioma and ovarian serous papillary carcinoma.