External quality assurance of HER2 FISH and ISH testing: three years of the UK national external quality assurance scheme.

The American Society of Clinical Oncology/College of American Pathologists guidelines highlighted the critical importance of quality assurance in diagnostic testing for HER2. Unstained formalin-fixed, paraffin-embedded human breast carcinoma cell line sections were circulated to scheme participants on 9 occasions. "Reference laboratories" reported results for the HER2/chromosome 17 ratio and HER2 copy number for 3 years for each cell line, including 418 sets of results (1,671 results total). The number of participants was 62 laboratories in the final analysis. The mean and SD of results from reference laboratories demonstrated consistency during the 3-year period. The percentage of laboratories achieving "appropriate" results ranged from 45% to 88%, and the percentage achieving "inappropriate" results ranged from 5% to 29%. No consistent effect of the HER2 in situ hybridization testing method was demonstrated. Participation in external quality assurance schemes is a valuable mechanism for demonstrating and acquiring consistency for HER2 testing by in situ hybridization. Poor performance can be corrected via assistance and advice.