[477] Insulin-Like Growth Factor II mRNA-Binding Protein 3 Is a Useful Marker To Distinguish Malignant Cells from Benign Mesothelial Cells in Serous Fluids

J Wang, MC Curtis, C Deng. Creighton University, Omaha, NE

Background: Insulin-like growth factor II mRNA-binding protein 3 (IMP3) is an oncofetal protein which plays important roles in varied critical biological processes, such as RNA trafficking and stabilization, cell growth, and cell migration. IMP3 is highly expressed in fetal tissue during embryogenesis but not in most adult tissues. Recent studies showed that IMP3 is over-expressed in a number of malignant tumors and that the expression of IMP3 is an independent prognostic factor for some malignancies. In addition, IMP3 can be used to distinguish benign from malignant lesions. Determining whether an effusion is malignant can be difficult in some cases. Therefore, we wanted to determine whether IMP3 might have diagnostic utility in the differentiation of benign mesothelial cells from malignant cells in serous fluids.
Design: Total 65 cases of pleural (30) and abdominal (35) effusion specimens with cell blocks were selected from the cytopathology files of the Department of Pathology at Creighton University Medical Center. The cytologic diagnoses of these cases included: adenocarcinoma (29), pseudomyxoma peritonei (PMP, 9), malignant mesothelioma (9), other malignancies (3), atypical cells (3), and negative for malignancy (12). Monoclonal anti-IMP3 antibody (Dako, clone 69.1, 1:200 dilution) was used to stain the tissue from the cell blocks and an isotype IgG2a was used as a negative control. The slides were reviewed by a senior pathology resident (J Wang) and a cytopathologist (C Deng), and IMP3 staining was graded as negative (no staining), weak (1+), moderate (2+), and strong (3+) positivity, based on the intensity of the cytoplasmic staining.
Results: Twenty-nine out of 29 (100%) adenocarcinomas were strongly positive for IMP3; 9 out of 9 (100%) malignant mesotheliomas were variably positive for IMP3 (1+ to 3+); 8 out of 9 (89%) PMP showed mild to moderate staining (1+ to 2+); 1 squamous cell carcinoma was negative; the other 2 malignant tumors were weakly and strongly positive respectively; 2 out of 3 cases with atypical cells were positive; only one of 12 (8%) benign fluids showed weak positivity for IMP3.
Conclusions: Our data indicates that IMP3 may be a useful marker to differentiate benign from malignant effusions. It may have particular diagnostic utility when atypical effusion cytology is encountered and the cells of interest do not possess clearly malignant features. Therefore, IMP3 should be included in an immunohistochemical staining panel to assist in distinguishing between benign and malignant effusions.
Category: Cytopathology

Wednesday, March 24, 2010 1:00 PM

Poster Session VI # 60, Wednesday Afternoon


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