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Automated Bright-Field Dual-Color In Situ Hybridization for MDM2: Interobserver Reproducibility and Correlation With
Gloria Zhang1, Christopher P Lanigan, John R Goldblum
1From the Departments of Anatomic Pathology (Drs Zhang and Goldblum) and Molecular Pathology (Mr Lanigan and Dr Tubbs), Robert J. Tomsich Pathology and Laboratory Medicine Institute, Cleveland Clinic, Cleveland, Ohio; and the Department of Pathology, Huntsman Cancer Center, University of Utah, Salt Lake City (Dr Downs-Kelly).
Dual-color, dual-hapten in situ hybridization (DDISH) accurately detects MDM2 amplification in tumors, showing high concordance with fluorescence in situ hybridization (FISH). This bright-field assay demonstrates excellent interobserver reproducibility among pathologists.
Area of Science:
- Oncology
- Molecular Pathology
- Genetics
Background:
- Atypical lipomatous tumors/well-differentiated liposarcomas are characterized by 12q13-15 region alterations, including MDM2 gene amplification.
- Detecting MDM2 amplification is crucial for differentiating these tumors from their histologic mimics, which lack this genetic alteration.
Purpose of the Study:
- To evaluate the interobserver reproducibility of the dual-color, dual-hapten in situ hybridization (DDISH) assay for MDM2 amplification.
- To assess the concordance between MDM2 DDISH and MDM2 fluorescence in situ hybridization (FISH).
Main Methods:
- 102 cases were analyzed using both FISH and DDISH for MDM2 amplification.
- MDM2 amplification was defined by an MDM2 to chromosome 12 ratio ≥ 2.0.
- Three pathologists, blinded to diagnoses and FISH results, independently scored the DDISH assays.
Main Results:
- The consensus DDISH diagnosis showed 98% concordance with FISH results.
- Individual reviewer agreement with MDM2 FISH was high (98–99%).
- Excellent interobserver agreement was observed among the three pathologists for DDISH scoring (κ = 0.949–0.95).
Conclusions:
- DDISH is a highly concordant method for assessing MDM2 copy number compared to FISH.
- The DDISH assay exhibits excellent interobserver reproducibility, even among pathologists with varied experience levels with bright-field assays.
