AIMS

Human epidermal growth factor receptor 2 (HER2) status of invasive breast cancers is vital for selection of patients for trastuzumab treatment. This study aimed to assess the level of agreement of HER2 status in core biopsy and excision specimens using immunohistochemistry, with in-situ hybridisation for equivocal cases.

METHODS AND RESULTS

300 consecutive invasive carcinomas with core biopsy and surgical specimens had HER2 assessed on both specimens. Immunohistochemistry was performed first. Fluorescence in-situ hybridization (FISH) was automatically performed if the immunohistochemistry was scored as equivocal (2+). There was agreement between the HER2 status of the two specimens in 294 tumours (98%). In two carcinomas the core was negative and the excision specimen showed focal strong staining with amplification. In four carcinomas the core biopsy was negative and the excision showed 2+ staining with amplification in at least one block (although in three there was no amplification in a second block).

CONCLUSION

There is excellent agreement between HER2 assessed in core biopsy and surgical specimens. Discrepancies arise most frequently due to focal amplification or levels of gene amplification around the cut-off for defining positivity.