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Expression of MDM2 and p16 in angiomyolipoma
Xiaoqi Lin1, William B Laskin2, Xinyan Lu1
1Department of Pathology, Northwestern University, Chicago, IL 60611.
Abstract:
Angiomyolipoma (AML) arises primarily from the kidney but may grow into the retroperitoneal space mimicking a primary retroperitoneal tumor. Fine needle aspiration (FNA) and core needle biopsy of AML, particularly the fat-predominant variant, may be difficult to distinguish from retroperitoneal well-differentiated liposarcoma (WDLS) or lipoma. Commonly used immunomarkers, MDM2 and p16, have proven useful in diagnosing WDLS and dedifferentiated liposarcoma (DDLS), while HMB45 and Melan-A are melanocyte-related markers characteristically expressed in AML. In this study, we investigated the utility of MDM2 and p16 along with HMB45 and Melan-A immunohistochemical analysis in distinguishing AML from WDL/DDLS or lipoma. Immunohistochemically, AMLs demonstrated focal MDM2 expression (40% of cases) and focal/diffuse expression of p16 (60%). AMLs marked focally or diffusely with HMB45 (76% of cases) and Melan-A (96%). These latter two immunomarkers were not expressed in any of the WDLS/DDLSs or lipomas tested. WDLS/DDLSs showed focal/diffuse expression of MDM2 (91% of cases) and p16 (97%). While focal expression of MDM2 and p16 was observed in 14% and 67% of lipomas, respectively, no lipoma exhibited diffuse MDM2 positivity. In our hands, MDM2 expression by itself cannot exclude the diagnosis of AML or lipoma, and p16 alone is not helpful in separating AML and conventional lipoma from WDLS/DDLS. However, along with morphology, an immunohistochemical battery including HMB45, Melan-A, MDM2 and p16 are useful in distinguishing AML from WDLS/DDLS or lipoma. For equivocal cases, fluorescence in situ hybridization for MDM2 should be performed.
Insights
Distinguishing kidney angiomyolipoma (AML) from retroperitoneal tumors like liposarcoma requires specific markers. HMB45 and Melan-A are key for AML, while MDM2 and p16 aid in diagnosing liposarcomas, especially when combined with morphology.
Area of Science:
- Pathology
- Oncology
- Immunohistochemistry
Background:
- Angiomyolipoma (AML) can present in the retroperitoneum, mimicking primary retroperitoneal tumors.
- Fat-predominant AMLs are challenging to differentiate from well-differentiated liposarcoma (WDLS) or lipoma using standard biopsies.
- Immunohistochemical markers like MDM2 and p16 are used for liposarcoma diagnosis, while HMB45 and Melan-A are characteristic of AML.
Purpose of the Study:
- To evaluate the diagnostic utility of MDM2, p16, HMB45, and Melan-A immunohistochemistry in differentiating renal AML from retroperitoneal WDLS/DDLS and lipoma.
- To determine the reliability of individual markers and combinations in distinguishing these entities.
Main Methods:
- Immunohistochemical analysis of AML, WDLS/DDLS, and lipoma samples using antibodies for HMB45, Melan-A, MDM2, and p16.
- Correlation of marker expression patterns with tumor morphology.
- Consideration of fluorescence in situ hybridization (FISH) for MDM2 in equivocal cases.
Main Results:
- AMLs showed high positivity for HMB45 (76%) and Melan-A (96%), which were negative in WDLS/DDLS and lipomas.
- WDLS/DDLS exhibited high positivity for MDM2 (91%) and p16 (97%).
- AMLs showed focal MDM2 (40%) and p16 (60%) expression; lipomas showed focal MDM2 (14%) and p16 (67%) expression, with no diffuse MDM2 positivity in lipomas.
Conclusions:
- HMB45 and Melan-A are reliable markers for identifying AML, being absent in WDLS/DDLS and lipoma.
- MDM2 and p16 alone are insufficient to exclude AML or lipoma, as they can show focal expression.
- A combined immunohistochemical panel including HMB45, Melan-A, MDM2, and p16, alongside morphology, is crucial for accurate differentiation. MDM2 FISH can be used for equivocal diagnoses.
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