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Abstract
HER2 testing in breast and gastric cancer is critical not only as a prognostic tool but also as a predictive marker for response to the humanized monoclonal antibody trastuzumab. Currently, HER2 status is assessed on histological and cytological specimens by conventional validated methods such as immunohistochemistry and FISH, while bright-field in situ hybridization techniques, such as silver in situ hybridization and chromogenic in situ hybridization, may offer performance benefits over FISH. The major points are first, technical issues, advantages and disadvantages relevant to each methods, and their clinical implications and second, the well-known genetic heterogeneity of HER2, and the occurrence of polysomy of chromosome 17. This review aims to summarize the growing body of literature on the accuracy of bright-field in situ techniques, notably silver in situ hybridization, in assessing HER2 status, and to discuss the role of such methods in pathology practice.
Acknowledgements
The authors would like to thank Mr. Michele Della Pace for his invaluable technical support.
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.
HER2 positivity (by overexpression and/or amplification) outlines a distinct biological and clinic-pathological cohort of breast and gastric cancers, which may benefit from target therapy.
Two diagnostic techniques are presently approved for assigning HER2 status in tumor samples: immunohistochemistry and in situ hybridization, and current guidelines suggest algorithms and scoring criteria to be applied in clinical practice to standardize results.
Among in situ hybridization techniques, bright-field silver in situ hybridization has been recently developed and enhanced as a suitable tool to be used in routine pathology laboratories, showing high accuracy as compared to FISH in several studies.
Optimal performance of the method requires continuous assessment of preanalytical, analytical and postanalytical phases, as well as quality control practices and proper training of the personnel involved.
Genetic heterogeneity and polysomy of chromosome 17 may represent critical issues in HER2 testing and need to be properly assessed and reported accordingly.