Introduction: An accurate determination of human epidermal growth factor receptor 2 (Her2) status in women with breast cancer is mandatory to identify patients who will benefit from trastuzumab-based therapy.
Materials and methods: Her2 immunohistochemical analysis (IHC) (performed with A0485 polyclonal antibody) on 943 invasive breast cancer cases was evaluated independently and blindly twice by 3 of us (V.A., I.P., and A.C.) according to DAKO scoring criteria. A total of 230 cases of invasive breast cancer scored 2+ at IHC and consequently evaluated by FISH were reviewed first independently, and then simultaneously by 3 of us (V.A., I.P., and A.C.) at a multiheaded microscope assessing the following parameters: overall signal intensity, granularity and continuity of membrane staining, and the presence of band-like membrane pattern in >25% of tumor cells. The frequencies of HER2 gene amplification for all the immunohistologic parameters (individually considered or in combination) were compared by Pearson χ analysis.
Results: Combinations of staining patterns did not give any statistically significant results, except when combining strong staining intensity and continuity of membrane signal. In fact, only 9 of the 86 cases with a weak-to-moderate staining intensity, which showed a fragmented membrane signal, resulted in being amplified by FISH, whereas 19 of the 51 cases presenting an overall strong IHC reaction and some extent of continuous membrane signal were FISH amplified (P=0.002).
Conclusions: Combined intensity and linearity of membrane signal, although limited, resulted in the best aid (P=0.0002) in making the final score decision in borderline IHC Her2 tests similar to what is envisaged in the Her2 scoring system for gastric cancer.