HER-2/neu protein expression in breast cancer evaluated by immunohistochemistry - A study of interlaboratory agreement

Immunohistochemistry (IHC) is used commonly for evaluating HER-2/neu protei n expression in breast cancer. Given the potential clinical importance of H ER-2/neu status in patient management, interlaboratory variability in HER-2 /neu IHC results is a matter of legitimate concern. We compared the results from 2 laboratories for HER-2/neu determined by IHC on paraffin sections o f the same 100 consecutive invasive breast cancers. Both laboratories used the same primary antibody; however, different methods for heat-induced epit ope retrieval (microwave or steam) and immunostaining (automated equipment from different manufacturers) and different scoring systems (positive-negat ive and 0-4+) were used. Slides were read in a blinded fashion and the resu lts from the 2 laboratories were compared. Of the 93 cases evaluable in bot h laboratories, 24% were scored as HER-2/neu-positive at 1 laboratory, and 23% were scored as positive at the other. Complete concordance in categoriz ation of HER-2/neu status between the 2 laboratories was achieved in 90 of 93 cases. Excellent interlaboratory agreement for HER-2/new IHC was attaine d suing the same primary antibody to HER-2/new, even without standardizatio n of assay method or scoring criteria. However, standardization of these pa rameters remains an important objective to optimize interlaboratory agreeme nt.