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To evaluate smooth muscle differentiation, myogenic markers [desmin, alpha-smooth muscle actin (SMA), and muscle-specific actin (HHF35)] have been widely used. Calponin and h-caldesmon, which are cytoskeleton-associated actin-binding proteins, have been reported to be more specific myogenic markers, especially since myofibroblasts express a small amount of h-caldesmon. Atypical fibroxanthoma (AFX) occurs in the sun-exposed skin of the elderly and follows a benign clinical course. Histologically, AFX, which is a pleomorphic spindle cell tumor and considered to be a superficial variant of malignant fibrous histiocytoma, also mimics leiomyosarcoma. AFX has been thought to differentiate along pathways with fibrohistiocytic and myofibroblastic phenotypes. AFX ( n=10), superficial leiomyosarcoma (S-LMS) ( n=17) and benign fibrous histiocytoma (BFH) ( n=17) were analyzed for myofibroblastic and smooth muscle differentiation immunohistochemically from the viewpoint of comparison. AFX and BFH showed immunoreactivities respectively for calponin (3/10, 11/17), desmin (3/10, 1/17), SMA (3/10, 13/17), and HHF35 (1/10, 5/17), but failed to express h-caldesmon (0/10, 0/17). S-LMS had a high immunoreactive rate of calponin (17/17), desmin (13/17), SMA (16/17), and HHF35 (16/17), while also expressing caldesmon (11/17). The results reveal that AFX and BFH have immunoreactivities for several myogenic markers, with myofibroblastic differentiation (calponin: +/-, h-caldesmon: -), but without the smooth muscle differentiation seen in S-LMS (calponin:+, h-caldesmon: +/-). In addition, calponin and h-caldesmon are considered to be useful markers for distinguishing AFX from S-LMS.

Three cases of rare low-grade endometrial stromal sarcoma of the extrauterine tissue are presented. Each one occurred in the ovary, pelvic and abdominal cavities. Two were associated with endometriosis. Histologically, the tumors were characterized by an infiltrative and diffuse proliferation of uniform round or oval cells, abundant small vessels, low mitotic activity, the presence of foam cells and vascular invasion. Immunohistochemically, all tumors expressed vimentin, muscle markers (desmin, muscle-specific actin and alpha-smooth muscle actin) and progesterone receptors. Two tumors were diploid and one was aneuploid by flow cytometry. All patients were well with no evidence of disease 16-39 months after surgery. It is suggested that this neoplasm may arise with or without endometriosis under hormonal influence. This rare variant of Müllerian tumors should not be confused with adenosarcoma and soft tissue tumors, such as smooth muscle tumors and solitary fibrous tumor.

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