Local Recurrence of Low-Grade Myofibroblastic Sarcoma of the Chest Wall: Report of a Case and Literatures Review

Discussion

LGMS is a rare soft tissue sarcoma and has generally been accepted as a unique tumor only in recent years^[1]. There have been 47 published cases summarized in a literature review^[2]. Among these cases, up to one third have a predilection for the soft tissue of the head and neck including the tongue, oral cavity and face. Others are located in extremities, trunk, retroperitoneum, bone, and breast. Primary sarcomas of the chest wall such as fibrosarcoma, liposarcoma, neurofibrosarcoma, dermatofibrosarcoma, malignant fibrous histiocytoma, and leiomyosarcoma are the most common tumor types. Yet there have been very few cases reported of LGMS arising in the chest wall that recurred locally.

The diagnosis of LGMS is usually made on clinical and pathological grounds, and the latter consist of morphology, immunohistochemistry and/or ultrastructure^[2,3]. Clinically, the tumors can recur locally and infrequently metastasize^[2]. Local recurrence in this case was documented after 34 months from the diagnosis of the primary lesion, which is consistent with the biological behaviour of LGMS. Morphologically, the tumors are composed mostly of spindleshaped cells with ovoid or tapered nuclear and scanty, or moderate amounts of eosinophilic cytoplasm. Tumor cells are arranged in fascicles, sheets or storiform whorls, with collagenous or myxoid stroma. Mitotic activity is variable, but abnormal mitotic figures are typically absent. Hemorrhage and necrosis are rare^[2]. The clinical and morphological features of our case served to exclude the diagnosis of a benign myofibroblastic disease.

Immunohistochemically, LGMS stains positively for at least one myoid marker. Frequently, this tumor is positive for a combination of several markers^[2,3]. As shown in our case, the tumor was positive for SMA, actin and desmin. Immunohistochemistry is especially important to differentiate LGMS from leiomyosarcoma, liposarcoma and fibrosarcoma. It has been suggested that the best way to diagnose LGMS is to demonstrate the ultrastructural features of spindle cells by electron microscopy^[3], but this examination is not always available for general diagnostic practice. Based on histopathology and immunohistochemistry, LGMS diagnosis can be made^[3]. According to the literature, nearly half of the reported cases (48.9%) were not examined by electron microscopy. Even in those cases in which electron microscopy was applied, not all had ultrastructural confirmation, and some had inconclusive ultrastructure^[2].

The primary lesion was interpreted as low-grade fibroblastic/myofibroblastic sarcoma, and in com-parison with the histopathological findings, between the primary and the recurrent lesion, remarkable histopathological overlap did exist. Although there are controversial issues surrounding the concept of a myofibroblastic sarcoma^[2,4], myofibroblasts do resemble fibroblasts, and it remains difficult to verify myofibroblastic differentiation without electron microscopy, There has been disagreement on the ultrastructure definition of the myofibroblast: a sarcoma fulfills criteria for a myofibroblastic sarcoma when it is composed primarily of myofibroblasts, but the relative proportion of myofibroblasts to fibroblasts has not been defined. All these features show the close relationship between myofibroblasts and fibroblasts. Furthermore, LGMS has been defined properly as a distinctive entity^[1]. This case of recurrence obviously occurred in the same anatomical region as the primary lesion, and was by a pathological examination to be composed predominantly of myofibroblasts, so the diagnosis of a local recurrence of LGMS was made.

Because LGMS is an uncommon disease, there are relatively few treated cases. Surgery, rather than radiotherapy, or chemotherapy is the main therapeutic modality^[3-5], and the latter two possible modalities are not very effective in treating this disease^[5]. Therefore en bloc resections were selected twice for her primary and recurrent lesions, without other treatment. So far the therapeutic results have been satisfactory.

Primary sarcoma of the chest wall is a rare disease, and LGMS widens the spectrum of diagnostic possibilities for the general thoracic surgeon facing a patient with a chest wall tumor.