Assessment of methods for tissue-based detection of the HER-2/neu alteration in human breast cancer: A direct comparison of fluorescence in situ hybridization and immunohistochemistry

Purpose: To compare the efficacy of fluorescence in situ hybridization (FIS H) and immunohistochemistry (IHC) in detecting the HER-2/neu alteration in human breast cancer. Patients and Methods: Unselected stage I, II, and III breast cancer patient s (N = 900) were tested for HER-2/neu gene amplification by FISH in paraffi n-embedded, formalin-fixed archival material. Of these samples, 856 were te sted for HER-2/neu overexpression by non-antigen-retrieval IHC with the pol yclonal antibody R60, the sensitivity and specificity of which wets prelimi narily compared with the United Stares Food and Drug Administration-approve d HercepTest (Dako Corp, Carpinterb, CA). Patient survival wets analyzed in relation to the presence of the HER-2/neu alteration as determined by thes e two methodologies. Results: A total of 189 (21%) of 900 patients were positive by FISH and 147 (17.2%) of 856 were positive by IHC. This discrepancy is consistent with e xpected loss of IHC sensitivity associated with tissue fixation/embedding. The HercepTest did not improve sensitivity and introduced false positives. Comparison of R60-based IHC with FISH demonstrates that patient survival is associated progressively to gene amplification level as determined by FISH , whereas for IHC an association is found only in the highest(3+) immunosta ining group. Among FISH-negative tumors, 45 (6.6%) of 678 were IHC-positive , with a survival probability similar to that of FISH-negarive/IHC-negative cases; FISH-positive/ IHC-negative patients have a survival probability si milar to that of FISH-positive/IHC-positive cases. Conclusion: IHC does not consistently discriminate patients likely to have a poor prognosis, whereas FISH provides superior prognostic information in segregating high-risk from lower-risk beast cancers. HER-2/neu protein over expression in the absence of gene amplification occurs infrequently in brea st cancer, in which case, patient outcome is similar to that of patients wi thout the alteration, (C) 2000 by American Society of Clinical Oncology.