HER2 Gene Amplification in Breast Cancer
HER2 Gene Amplification in Breast Cancer
International and national guidelines highlight the importance of accuracy, reproducibility, and quality control of in situ hybridization (ISH) methods for testing breast carcinomas. However, few guidelines cover the reporting of ISH cases with "unusual" signal patterns, including, eg, heterogeneity and loss of chromosome enumeration probe or gene signals. These cases are, in fact, relatively frequent, and there is a need for developing evidence- or consensus-based reporting guidelines to ensure consistency of treatment.
Following an audit of cases from a single center (including >1,700 cases) we show that approximately 10% of ISH results reflect unusual signal patterns. We illustrate the most common of these patterns and provide reporting guidelines for diagnosticians and recommendations for future research. Our goal is to ensure that in the future such "rogues" are reported in a consistent manner that, ultimately, will be supported by molecular and biochemical evidence.
HER2 gene amplification has been recognized for many years as a poor prognostic indicator in early breast cancer. More recently, with the introduction of HER2-targeted therapies, in particular trastuzumab (Herceptin), HER2 status has become a critical component in selecting the best treatment options in early and advanced breast cancer. The use of fluorescent in situ hybridization (FISH) and other in situ hybridization (ISH)-based methods, eg, chromogenic and silver ISH, has become widely accepted as the "gold standard" for determining HER2 amplification status and, in most cases, provides a clear answer as to whether a case is amplified; however, there are small subsets of "unusual" cases that do not conform to conventional diagnostic guidelines and reporting procedures and provide significant interpretive difficulties.
The current gold standard for assessing HER2 amplification is to calculate the mean ratio of HER2/chromosome enumeration probe (CEP)17 in 20 to 60 cells with a mean ratio of greater than 2.0 classed as amplified and a ratio of less than 2.0 as HER2–. With our increasing experience with ISH come increasing numbers of cases that do not conform to the expected patterns described in publications and reporting guidelines. These raise questions about the underlying cytogenetic changes and their implications in determination of HER2 status. These anomalies take many forms and include heterogeneity, loss of signals, variations in signal size, and colocalization of HER2/CEP17 signals.
We recently updated the UK HER2 guidelines with a specific focus on the approaches to interpretation of HER2 gene amplification on ISH and also performed an audit of the impact of heterogeneous HER2 amplification, with information on the frequency and prognostic impact of different cutoffs for HER2 gene amplification. We recognize, however, that there are additional aspects of HER2 ISH interpretation that present diagnostic and interpretive challenges. An update to UK guidelines recommends that these difficult cases be analyzed by 2 observers. In the current study, we sought to identify the frequency and describe reporting of specific examples of challenging cases—the "rogues" that provoke intense discussion at multidisciplinary meetings. This article describes the most commonly occurring cases from this HER2 rogues gallery and provides recommendations on how these should be interpreted. Future reports may address less frequently occurring abnormalities.
It should be recognized that as with most guidelines, these recommendations reflect our expertise and are subject to change with emerging evidence. However, we are acutely aware that, for the majority of these unusual cases, representing in total almost 10% of HER2 breast cancers assessed by ISH, there is no likelihood of a robust evidence base (within the context of a clinical trial) that will determine treatment efficacy with HER2-directed therapies. There may be research questions that, in the future, further inform the interpretation of these cases, and, when these are likely to do so, we have made suggestions for such research.
Abstract and Introduction
Abstract
International and national guidelines highlight the importance of accuracy, reproducibility, and quality control of in situ hybridization (ISH) methods for testing breast carcinomas. However, few guidelines cover the reporting of ISH cases with "unusual" signal patterns, including, eg, heterogeneity and loss of chromosome enumeration probe or gene signals. These cases are, in fact, relatively frequent, and there is a need for developing evidence- or consensus-based reporting guidelines to ensure consistency of treatment.
Following an audit of cases from a single center (including >1,700 cases) we show that approximately 10% of ISH results reflect unusual signal patterns. We illustrate the most common of these patterns and provide reporting guidelines for diagnosticians and recommendations for future research. Our goal is to ensure that in the future such "rogues" are reported in a consistent manner that, ultimately, will be supported by molecular and biochemical evidence.
Introduction
HER2 gene amplification has been recognized for many years as a poor prognostic indicator in early breast cancer. More recently, with the introduction of HER2-targeted therapies, in particular trastuzumab (Herceptin), HER2 status has become a critical component in selecting the best treatment options in early and advanced breast cancer. The use of fluorescent in situ hybridization (FISH) and other in situ hybridization (ISH)-based methods, eg, chromogenic and silver ISH, has become widely accepted as the "gold standard" for determining HER2 amplification status and, in most cases, provides a clear answer as to whether a case is amplified; however, there are small subsets of "unusual" cases that do not conform to conventional diagnostic guidelines and reporting procedures and provide significant interpretive difficulties.
The current gold standard for assessing HER2 amplification is to calculate the mean ratio of HER2/chromosome enumeration probe (CEP)17 in 20 to 60 cells with a mean ratio of greater than 2.0 classed as amplified and a ratio of less than 2.0 as HER2–. With our increasing experience with ISH come increasing numbers of cases that do not conform to the expected patterns described in publications and reporting guidelines. These raise questions about the underlying cytogenetic changes and their implications in determination of HER2 status. These anomalies take many forms and include heterogeneity, loss of signals, variations in signal size, and colocalization of HER2/CEP17 signals.
We recently updated the UK HER2 guidelines with a specific focus on the approaches to interpretation of HER2 gene amplification on ISH and also performed an audit of the impact of heterogeneous HER2 amplification, with information on the frequency and prognostic impact of different cutoffs for HER2 gene amplification. We recognize, however, that there are additional aspects of HER2 ISH interpretation that present diagnostic and interpretive challenges. An update to UK guidelines recommends that these difficult cases be analyzed by 2 observers. In the current study, we sought to identify the frequency and describe reporting of specific examples of challenging cases—the "rogues" that provoke intense discussion at multidisciplinary meetings. This article describes the most commonly occurring cases from this HER2 rogues gallery and provides recommendations on how these should be interpreted. Future reports may address less frequently occurring abnormalities.
It should be recognized that as with most guidelines, these recommendations reflect our expertise and are subject to change with emerging evidence. However, we are acutely aware that, for the majority of these unusual cases, representing in total almost 10% of HER2 breast cancers assessed by ISH, there is no likelihood of a robust evidence base (within the context of a clinical trial) that will determine treatment efficacy with HER2-directed therapies. There may be research questions that, in the future, further inform the interpretation of these cases, and, when these are likely to do so, we have made suggestions for such research.