ABSTRACT
<p><b>OBJECTIVE</b>To study the clinicopathologic characteristics of extrarenal malignant rhabdoid tumor (E-MRT) with emphasis on diagnosis and differential diagnosis.</p><p><b>METHODS</b>The clinical and pathologic data of 8 E-MRT cases were reviewed. The outcome was analyzed.</p><p><b>RESULTS</b>There were four males and four females. The age at presentation ranged from 3 days to 8 years (mean, 2.6 years; median, 3 years). The tumors were located in the extremities (n = 1), head and neck (n = 2), trunk (n = 2), cervical cord (n = 1), liver (n = 1) and retroperitoneum (n = 1). Histologically, the tumors were composed of a diffuse proliferation of rounded or polygonal cells with eccentric nuclei, prominent nucleoli, and glassy eosinophilic cytoplasm containing hyaline-like inclusion bodies, arranged in sheets and nests. Cellular atypia was easily observed and mitotic activity was high. Necrotic and hemorrhagic areas were abundant. On immunohistochemistry, the tumor cells expressed vimentin and epithelial marker such as EMA, AE1/AE3, and CAM5.2. The absence of INI1 protein expression was a distinctive feature. Follow-up of all eight cases revealed five deaths in one year and the other three were disease-free at last follow-up of one month, three months and seven months.</p><p><b>CONCLUSIONS</b>E-MRT is a rare and highly aggressive tumor of infancy and childhood. Recurrence and distant metastasis was common and the 5-year survival rate is low. Increased awareness of the clinocopathologic features and immunophenotypes of E-MRT is helpful for correct diagnosis and effective treatment.</p>