[1564] Malignant Rhabdoid Tumors: A 12 Year Experience
S Bishu, BD Bolton, V Rajaram, PM Chou. Northwestern University Feinberg School of Medicine, Chicago, IL; Children's Memorial Hospital, Chicago, IL
Background: Malignant rhabdoid tumors (MRT) are rare childhood neoplasms. Although originally described in the kidney, these tumors have now been identified in various locations including the liver, soft tissue, and the central nervous system. The purpose of this study was to review the clinicopathologic features of rhabdoid tumors identified over a 12 year period at a tertiary pediatric medical center, and also to stress the proper classification of these tumors as currently more aggressive therapy has led to improved survival.
Design: A retrospective review from January 1st,1996 to September 10th, 2008 identified 20 patients who were diagnosed with MRT. These patients were analyzed: age at diagnosis, site of tumor, histology, immunohistochemical profile, and mortality.
Results: MRT were identified in 10 males and 10 females. The median age at diagnosis was 27.5 months. The lesions were located in a wide variety of anatomic sites including CNS (9), liver (2), kidney (2), mediastinum (1) and soft tissue (6). Histologically, most tumors were 
Malignant small blue cell tumors
, and the majority showed at least focal rhabdoid morphology. Immunohistochemical stains showed characteristic poly phenotypic pattern: positive for vimentin, cytokeratin/epithelial membrane antigen (EMA) and smooth muscle actin (SMA) in all cases. Some MRTs showed scattered positivity for GFAP, CD31, CD34, CD117, CD99 and Myogenin. BAF-47 staining showed loss of normal nuclear positivity in tumor cells of all cases. Clinically, prior to 2006, most patients (7 of 9) died of disease, and one had metastasis despite treatment. Since 2006 one patient was lost to follow up, and only 2 patients have died (one soft tissue, one kidney). The remaining patients have undergone treatment with a more aggressive chemotherapy with or without radiation, and as of date have no evidence of recurrence or metastasis.
Conclusions: In our experience, MRT present with varied morphology and do not always show classic rhabdoid features. The tumors show polyphenotypic immunostaining pattern and loss of normal nuclear positivity for BAF-47. With recent changes in therapeutic approach, over 50% of our patients have longer survival. Because of the varied morphology and immunophenotypic expression, use of restricted immunostains could result in a misdiagnosis. It is therefore important to consider this tumor in the differential diagnosis for all Malignant small blue cell tumor, emphasizing the need to perform BAF47 immunostaining in all cases.
Category: Pediatrics
Monday, March 9, 2009 1:00 PM
Poster Session II # 209, Monday Afternoon