Comparison of HER2/neu status assessed by quantitative polymerase chain reaction and immunohistochemistry

We prospectively evaluated a series of 254 breast cancers by quantitative p olymerase chain reaction (PCR) and immunohistochemistry using 3 antibodies: HercepTest, CB11, and TAB250. DNA was extracted from a 10-mum tumor sectio n for PCR, and 4-mum serial sections were taken from the same block for imm unohistochemistry. The immunohistochemical results were scored using a semi quantitative immunohistochemical system. A positive tumor by immunohistoche mistry had a score of 5 or more. The manufacturer's recommended scoring sys tem was used for the HercepTest. Tumors were positive for gene amplificatio n if the ratio of the HER2/neu gene to control gene after normalization was 2 or more. Of 254 cases, 61 showed gene amplification. For immunohistochem istry, 23% of tumors were positive with CB11, 27% with TAB250, and 37% with the HercepTest. Results for each antibody were compared with PCR results. The overall concordance for the HercepTest was 82%, which was significantly lower than that for CB11 (88%) or TAB250 (87%). The specificity for the He rcepTest was 80% compared with 90% for TAB250 and 93% for CB11, while the p ositive predictive value for the HercepTest was 57% compared with 71% and 7 6% for TAB250 and CB11, respectively.