Impact of 2013 American Society of Clinical Oncology/College of American Pathologist guidelines on borderline immunostaining results for HER2: a retrospective study on HER2 FISH results in 1 780 cases of invasive breast cancers

Objective: To analyze the impact of the revised 2013 American Society of Clinical Oncology/College of American Pathologist(ASCO/CAP)HER2 testing guidelines on the status of HER2 and its clinical significance in invasive breast cancers by fluorescent in situ hybridization(FISH).

Methods: One thousand seven hundred and eighty invasive breast cancer cases with equivocal 2+ immunostaining detected by FISH were retrospectively selected from 2010 to 2014, and the HER2/CEP17 dual-probe results were evaluated according to both the 2007 and 2013 ASCO/CAP guidelines for comparative analysis.

Results: Among the 1 780 IHC HER2 (2+ ) invasive breast cancers, the number of HER2 positive, equivocal and negative case were 310(17.41%), 66(3.71%)and 1 404(78.88%) respectively, basing on the 2007 guidelines; whereas basing on the 2013 ASCO/CAP HER2 guidelines, the number of HER2 positive, equivocal and negative case was 360 (20.22%), 182 (10.23%)and 1 238 (69.55%) respectively. Compared with the 2007 guidelines, the proportion of positive and equivocal cases were higher in the 2013 guidelines (17.41% versus 20.22%, 3.71% versus 10.23% respectively), while the proportion of negative cases was lower(78.88% versus 69.55%).

Conclusions: Using the 2013 ASCO/CAP guidelines could lead to an increase in positive and equivocal cases, and a decrease in negative cases. The increase can probably be attributable to the inclusion of HER2 copy number besides HER2/CEP17 ratio as positive criteria, and it improves the accuracy and may be of important value for screening more population who benefit from HER2 targeting treatment; however the benefits for HER2 positive with low HER2 copy number and the clinical significance of the equivocal cases need to be further investigated.