Evaluation of immunohistochemical expression of MDM2 protein in comparison with MDM2 gene amplification in diagnosing lipomatous tumors

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Abstract

Objective

Our goal was to compare the immunohistochemical detection of murine double minute 2 (MDM2) protein and MDM2 gene amplification in diagnosing adipose tissue tumors.

Materials and methods

MDM2 protein expression was examined by immunohistochemistry in formalin-fixed paraffin-embedded tissue samples from 67 benign and malignant adipose tumors. The immunostaining findings were correlated with the MDM2 amplification status by differential PCR.

Results

MDM2 immunopositivity was detected in 3.8% lipoma, 70.6% well-differentiated liposarcomas (LPS), and 75% of dedifferentiated LPS with significant difference. MDM2 amplification occurred in 21 out of the 27 (56%) positive cases for MDM2 protein expression. MDM2 amplification was found more frequently in well-differentiated LPS (58.8%) and dedifferentiated LPS (62.5%) in comparison with the pleomorphic or myxoid variants. Overall, the MDM2 positivity was not associated with MDM2 amplification in six out of 27 (22.2%) cases, whereas 21 (77.8%) of the MDM2 amplified cases displayed nuclear immunoreactivity with anti-MDM2 antibodies. A highly significant correlation was obtained between MDM2 protein expression and gene amplification.

Conclusion

Evaluation of MDM2 amplification using differential PCR may be used to supplement the immunohistochemical analysis of MDM2 protein when the diagnosis of adipose tissue tumors is not possible based on the clinical and histologic information alone.

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