[1803] Oncofetal Protein IMP3, a New Biomarker To Distinguish Malignant Mesothelioma from Reactive Mesothelial Proliferation.

Min Shi, Armando Fraire, Peiguo Chu, Kristine Cornejo, Bruce Woda, Zhong Jiang. UMass Memorial Medical Center and University of Massachusetts Medical School, Worcester; City of Hope National Medical Center, Los Angeles, CA

Background: Distinguishing malignant mesothelioma (MM) from a benign reactive mesothelial proliferation remains a major challenge for surgical pathologists. No reliable diagnostic biomarker has been found to distinguish between malignant and reactive mesothelial cells. In this study, we investigated whether IMP3, an oncofetal protein, can be used as a diagnostic biomarker to distinguish between these two entities.
Design: A total of 109 cases (MM, n=45; reactive mesothelial cells, n=64) obtained from the formalin-fixed, paraffin-embedded block archives of two tertiary medical centers were examined by immunohistochemistry for IMP3 expression. Among the MM, 27 (60.0%) cases were epithelial type, 10 (22.2%) cases were mixed type and 8 (17.8%) were sarcomatous type. All cases were collected between January of 1997 and April 2010, and the diagnoses were confirmed by at least two pathologists.
Results: IMP3 showed strongly cytoplasmic staining in 33 of 45 (73%) MM cases. In contrast, none of 64 cases (0%) of benign reactive mesothelial proliferation exhibited IMP3 expression. Among the IMP3 positive MM, 27 (82%) exhibited diffuse IMP3 expression in more than 50% of malignant cells, 2 (6%) in 25-50% of malignant cells, and 4 (12%) in 5-25% of malignant cells. There was a positive IMP3 expression in 21/27 (78%) of epithelial, 8/10 (80%) of mixed and 4/8 (50%) of sarcomatous type. Importantly, two cases which were previously diagnosed as atypical mesothelial proliferation but were confirmed to be MM later showed IMP3 positivity in more than 50% of malignant cells.
Conclusions: Our findings indicate that IMP3 is a sensitive and specific biomarker for malignant mesothelioma and can separate malignant mesothelioma from a reactive mesothelial proliferation. Expression of IMP3 can increase the level of confidence in establishing the diagnosis of malignant mesothelioma.
Category: Pulmonary

Tuesday, March 1, 2011 1:15 PM

Platform Session: Section F, Tuesday Afternoon


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