Context: Human epidermal growth factor receptor 2 (HER2) status of breast carcinomas is usually determined by immunohistochemical (IHC) staining and, if the IHC results are equivocal, in situ hybridization (ISH). Multiple ISH tests are sometimes required for multiple primary or metastatic tumors. A method for multiplex ISH test on tissues from multiple blocks is helpful in these situations.
Object: To evaluate the clinical application of transferred-tissue microarray (TTM) followed by a dual-probe HER2 fluorescence in situ hybridization (FISH).
Design: A 3×3 TTM technique was successfully established using 152 invasive mammary carcinoma tissue fragments. To evaluate detection of HER2 positive tumors, this cohort was enriched with tumors with IHC scores of 2 and 3.
Results: The HER2 FISH analyses revealed that all transferred-tissue fragments were adequate for determining HER2 amplification. Tissue loss was minimal and had no major adverse effects on interpretation of the test results. Of the 81 tumors with IHC scores of 3, 72 (88.8%) were positive for HER2 FISH. The remaining tumors were negative for HER2 FISH in both TTM and reflex whole tissue section. Finally, FISH results for tumors with IHC scores of 2 were compared between TTM and whole tissue section. Concordance was high in overall positivity/negativity (100%), HER2 copy number (97.5%), and HER2/CEP17 ratio (100%).
Conclusions: This novel technique is a reliable option for performing multiple HER2 FISH tests simultaneously in clinical and research-oriented settings with less tissue damage compared with conventional tissue microarray techniques.