Abstract and Introduction
Abstract
Introduction: The status of the gene encoding human EGF-like receptor 2 (HER2) is an important prognostic and predictive marker in breast cancer. Only breast cancers with HER2 amplification respond to the targeted therapy with trastuzumab. It is controversial to what degree the primary tumour is representative of distant metastases in terms of HER2 status. Discrepancies in HER2 status between primary tumours and distant metastases have been described, but their reasons remain unclear. Here, we compared HER2 status on cytological specimens of distant metastases with the result from the primary carcinomas, and explored the prevalence of and the reasons for discrepant results.
Methods:HER2 status was determined by fluorescence in situ hybridisation. HER2 gene amplification was defined as a HER2/chromosome 17 signal ratio of 2 or more. HER2 results from cytological specimens of matched distant metastases were compared with the results from the corresponding primary tumours (n = 105 patients). In addition, lymph node metastases were analysed in 31 of these patients.
Results:HER2 amplification was found in 20% of distant metastases. HER2 status was discordant between the primary tumour and distant metastasis in 7.6% of the 105 patients. Re-evaluation revealed that in five patients (4.7%), discrepancies were due to interpretational difficulties. In two of these patients, focal amplification had initially been overlooked as a result of heterogeneity in the primary tumours or in the metastases, respectively. A further three patients had borderline amplification with a ratio close to 2. Discrepancy remained unexplained in three patients (2.9%).
Conclusion:HER2 gene status remains highly conserved as breast cancers metastasise. However, discrepant results do occur because of interpretational difficulties and heterogeneity of HER2 amplification. Cytological specimens from distant metastases are well suited for HER2 fluorescence in situ hybridisation analysis.
Introduction
The HER2 oncogene encodes a transmembrane tyrosine kinase (human EGF-like receptor 2) located on chromosome 17q21. HER2 protein belongs to the epidermal growth factor family and is important for cell differentiation, adhesion and motility.HER2 gene amplification and protein overexpression exists in about 20% of breast cancers and is linked to a poor prognosis. From a clinical point of view, HER2 receptor has become important as a target for antibody-based therapy with trastuzumab (Herceptin). Trastuzumab was originally approved for the treatment of metastatic HER2-positive breast cancers because of a significant survival benefit when given in combination with paclitaxel. More recently, adjuvant treatment of primary, HER2-positive breast cancers with trastuzumab has been shown to improve patient outcome markedly. Thus, determination of HER2 status in every breast cancer patient to select for adjuvant treatment with trastuzumab is becoming a standard worldwide. There has been much debate on how to test HER2 status. Other than fluorescence in situ hybridisation (FISH), immunohistochemistry is liable to technical and interpretational variability. Accordingly, it has been shown that response to trastuzumab is strongly associated with HER2 gene status irrespective of protein expression determined by immunohistochemistry. Importantly, no standardised immunocytochemical assay is available for cytological specimens. For these reasons, testing the HER2 gene status by FISH is now widely regarded as the gold standard.
HER2 status is commonly determined in the primary tumour, because biopsies from metastasised lesions are not always available. In three previous FISH studies on 12 to 68 patients, the prevalence of a discrepant result between the primary breast cancer and the distant metastasis ranged from 0% to 22.2%.
Because of the controversial data and the therapeutic importance of HER2 testing, we compared the HER2 status in a large series of primary breast cancers and their matched distant metastases by FISH. In addition, we attempted to elucidate reasons for these discrepancies.
Our results demonstrate that discrepancies in HER2 gene status between primary breast cancers and matched metastases do occur and may be related to technical and interpretational difficulties.