h-caldesmon, a novel smooth muscle-specific antibody, distinguishes between cellular leiomyoma and endometrial stromal sarcoma

The difficulty in distinguishing between smooth muscle and endometrial stro mal-derived neoplasms of the uterine corpus is a notorious and clinically r elevant problem in pathology of the female genital tract. Immunohistochemis try offers some aid in resolving this difficulty, because the expression of smooth muscle markers is reputed to indicate smooth muscle derivation. Thi s expression, however, is not entirely specific, and difficult cases may st ill present in which immunohistochemistry is of little help. To explore thi s problem, the authors evaluated the expression of traditional muscle marke rs and high-molecular-weight caldesmon (h-cal), an actin and tropomyosin bi nding protein that has recently been described as a useful muscle marker, i n uterine leiomyosarcoma (LMS), cellular leiomyomata (CL), and endometrial stromal sarcoma (ESS). Formalin-fixed and paraffin-embedded tissue sections from nine LMSs, 11 CLs, and 12 ESSs were evaluated with commercially avail able monoclonal antibodies against smooth muscle actin (SMA), desmin, and h -cal. Established morphologic criteria were used to classify the neoplasms. We found that there was, as expected, a significant difference in the expr ession of traditional smooth muscle markers (SMA and desmin) between tumors derived from smooth muscle and those derived from endometrial stroma (p = 0.005 for LMS and 0.013 for CL). We further found that h-cal was most usefu l in distinguishing between CL and ESS (p = 0.01). A significant difference between h-cal expression in LMS versus ESS was not found. Of note. one ESS expressed both SMA and desmin but lacked h-cal expression. Our findings co nfirm the most useful immunohistochemical data to date; smooth muscle neopl asms are generally distinguishable from endometrial stromal tumors by the e xpression of conventional muscle markers. We also report here that h-cal is useful more specifically in the differentiation of CL from ESS.