Immunohistochemical analysis of the monoclonal antibody 4B5 in breast tissue expressing human epidermal growth factor receptor 4 (HER4)

Aims A recent study examining the specificity of human epidermal growth factor receptor ( HER ) 2 pharmacodiagnostic antibodies demonstrated that CB 11 and 4B5 stain both HER 2 ‐transfected and HER 4 ‐transfected cell lines. However, there has been no evidence showing that 4B5 has affinity for HER 4 in clinically obtained tissues, and, if so, whether this has any impact on the assessment of HER 2. We therefore sought to determine the expression of membrane‐bound HER 4 in clinical breast carcinomas, and evaluate its impact on the clinical utility of 4B5 in determining HER 2 status. Methods and results Breast carcinomas were assessed by immunohistochemistry ( IHC ) for membrane‐bound HER 4 using anti‐ HER 4 clone E200. HER 2 expression in these cases was then assessed using anti‐ HER 2 clone 4B5, and a reference clone, SP 3. In all 117 membrane HER 4‐positive cases (out of 241), 4B5 scored equal to or less than the reference anti‐ HER 2 clone SP 3. Eighteen cases were positive for membrane‐bound HER 4 by E200 and negative by 4B5, including a membrane HER 4 level 3+ case. Conclusions No cross‐reactivity of 4B5 with membrane‐bound HER 4 was identified in the clinical IHC analysis of formalin‐fixed paraffin‐embedded breast carcinoma cases as evidenced by the HER 4 antibody clone E200.