Unique cell membrane expression of topoisomerase‐II alpha as a useful diagnostic marker of liposarcoma

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Abstract
Topoisomerase‐II alpha (Topo‐II alpha) is known as a cell cycle‐related intranuclear marker. To the best of our knowledge, the expression of Topo‐II alpha on extranuclear sites has not been reported. The aim of the present study was to determine the usefulness of Topo‐II alpha immunostaining for detecting the lipoblasts that are essential to diagnosing liposarcoma. Surgical specimens, including benign lipomatous tumors (four cases), well‐differentiated liposarcomas (three cases), myxoid liposarcomas (six cases), pleomorphic liposarcomas (two cases), dedifferentiated liposarcomas (two cases), myxoid malignant fibrous histiocytomas (six cases), and one case of mesenteric panniculitis, were studied. Samples were immunostained using antibodies for Topo‐II alpha, S‐100 protein and Ki‐67. In addition, we used the western blot method to investigate immunohistochemical‐affinity in adipocytes. Mature adipocytes and lipoblasts in all of the benign and malignant lipomatous tumors intensively expressed cell contours positivity for Topo‐II alpha. Cytoplasm of the lipoblasts occasionally reacted to the antibody and highlighted intracytoplasmic small unilocular, multivacuolated, or bubble‐like patterns. Western blot analysis confirmed a 70 kDa product reactive to Topo‐II alpha in the cell membrane fragment of mature adipocytes. S‐100 protein expressed adipocytes and lipoblasts, but the detection of lipoblasts was not as easy as in Topo‐II alpha immunostaining. Immunoreactivity of Ki‐67 was limited to the nuclei, and the nuclear labeling index of Ki‐67 correlated with that of Topo‐II alpha. The immunoreactivity of Topo‐II alpha for lipoblasts was more sensitive and obvious than those of S‐100 protein. Immunostaining using the antibody for Topo‐II alpha seems to be useful in recognizing lipoblasts that have been overlooked in hematoxylin–eosin‐stained preparations, and is a useful marker for diagnosing liposarcoma.