Anatomical pathologyDetermining HER2 (ERBB2) amplification status in women with breast cancer: final results from the Australian in situ hybridisation program
Introduction
Human epidermal growth factor receptor 2 (HER2) signalling regulates cell growth, division and repair. Between 10 and 35% of breast cancers have amplification of this gene,1, 2, 3, 4, 5 the higher percentages being seen among recurrent and metastatic tumours. Amplification of HER2 is associated with rapid tumour proliferation, and reduced progression-free and overall survival.6, 7, 8 Trastuzumab (Herceptin) is a monoclonal antibody directed against HER2. It has been shown to inhibit the proliferation of human tumour cells that overexpress HER2, and was first approved for use in Australia in 2000. There are proven survival benefits in women with HER2 positive breast cancer who are treated with trastuzumab, both in early breast cancer9, 10, 11, 12, 13, 14, 15, 16, 17 and in metastatic disease.18, 19, 20, 21, 22 Evaluation of the HER2 status of all breast cancers at diagnosis is essential in order to predict the potential benefit from trastuzumab, lapatinib, trastuzumab-emtansine (TDM-1), pertuzumab and other anti-HER2 therapies.23, 24, 25 Despite requirements for diagnostic testing in order to access treatment, there continue to be challenges in accurate determination of HER2 status.26
HER2 testing can be routinely performed either using immunohistochemistry (IHC) or by in situ hybridisation (ISH). There has been some debate around whether use of IHC alone is sufficient to accurately determine HER2 status;25 however, it is generally accepted that IHC 0 or 1+ is considered HER2 negative, and IHC 3+ is considered HER2 positive, with those samples with IHC 2+ being equivocal and requiring retesting by ISH.23, 24, 25, 27, 28 However, initial ISH testing does not always provide a definitive result. These non-diagnostic (indeterminate) and remaining equivocal specimens cause uncertainty amongst clinicians about the best treatment option for their patient.29
In Australia, approximately 15,000 new cases of breast cancer are diagnosed annually.30 In line with international standards, the equivocal chromogenic ISH (CISH or SISH) cases in Australia are referred to a large central testing laboratory for fluorescent ISH (FISH) testing in the hope of obtaining a definitive result (Fig. 1). However, unlike most jurisdictions that rely on both IHC and ISH (for example Canada, USA and Europe), in Australia subsidised access to trastuzumab for patients with early or locally advanced breast cancer is limited to those who have demonstrated HER2 positivity by ISH.31 Patients with HER2 positive early breast cancer confirmed by immunohistochemistry (IHC) alone are not eligible for subsidised treatment with trastuzumab, although they can access the treatment privately.32 Given the requirement for HER2 ISH testing of each new case of early breast cancer in order to gain access to trastuzumab, the Australian in situ hybridisation program was established. The program was developed as a national, multicentre, coordinated project, sponsored by Roche Products Pty Ltd (Australia) and was overseen by the Australian HER2 Testing Advisory Board. Its primary aim was to provide accurate tumour HER2 ISH testing for all women diagnosed with early breast cancer. Details about the establishment of the program,33 and selected results from October 2006 to September 2010 have been reported previously.34 Here we report the final details of the HER2 positivity rates, and IHC/ISH correlation recorded across Australia from October 2006 until April 2012, at which time the program was closed, and funding was taken over by the Australian government.
Section snippets
Methods
The methods used in this study have been published previously.33 Briefly, samples were collected from patients aged 18 or over with early breast cancer or metastatic breast cancer. These samples were tested by IHC for HER2 overexpression by local laboratories. They were then referred to one of 30 reference laboratories for ISH testing, where analysis was performed by anatomical pathologists with specialised training in ISH testing and an interest in breast pathology. Results of these tests
Results
At the time of study closure, there were 30 laboratories functioning as ISH testing laboratories, spread across seven Australian States or Territories. Of these, 24 were using SISH (Ventana) and six were using CISH (Invitrogen).
Discussion
This study describes the final outcomes of the largest reported ‘real-world’ testing program employing ISH determination of HER2 status of early and metastatic breast cancers. From September 2006, HER2 ISH testing was made available to all Australian patients with breast cancer, and by completion of the program, was considered standard of care. The downshift in HER2 positivity rates in early breast cancer reflects a shift in practice from initial triage with IHC to the use of ISH testing for
Conclusion
Appropriate and accurate determination of HER2 status in women with breast cancer is important for making treatment decisions. Our data indicate that universal SISH/CISH testing with centralised FISH testing for non-diagnostic or equivocal cases can result in successful determination of HER2 status in >99.9% of patients. This is a successful story of a cohesive service for determining HER2 status in women with breast cancer in a ‘real-world’ setting.
Acknowledgements
The authors would like to thank Dr Belinda Butcher, WriteSource Medical Pty Ltd for medical writing assistance. All authors reviewed, revised and approved the manuscript prior to submission. The authors would also like to thank all the laboratories and personnel involved in this study.
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