Multisite phosphotyping of the ErbB-2 oncoprotein in human breast cancer

Background: Overexpression of the ErbB-2 (HER2/neu) receptor tyrosine kinas e is one of the most common molecular changes in human cancer, but the func tional significance of this phenotype remains uncertain. Methods and Results: Using phosphorylation-specific antibodies recognizing different ErbB-2 functional states, we assessed the phosphorylation status of ErbB-2 in 102 human breast cancer specimens. Quantitative ErbB-2 immunob lotting intensity correlated directly with that of immunohistochemistry (r = 0.84). Widely varying phosphorylation profiles were evident in 65 ErbB-2- positive carcinomas, suggesting different ErbB-2 functions in different tum ors. In a subset of patients for whom clinical data were obtainable, mortal ity trends were strongly associated with the quantitative signal intensitie s of ErbB-2 phosphoantibodies (P less than or equal to .02), but not with t hose of conventional antibodies to ErbB-2 (P = .147), epidermal growth fact or receptor (r = .44), or phosphotyrosine (P = .94). Conclusion: Although requiring corroboration in larger prospective clinical studies, these findings suggest that immunophenotyping using phosphorylati on-specific antibodies may enable more accurate prediction of cancer behavi or than is currently obtainable using conventional reagents.