ERBB2 and breast cancer: For example, inlocalized or metastatic breast cancer, tumor biology, including hormone sensitivity,HER2 status, cellular differentiation, and proliferation index, isfundamental to decision making and treatment planning.6 These variables also provide prognostic informationregarding average overall survival and tumor recurrence, both for patients anddoctors.4-9 Moreover, current guidelines, including those of ASCO,the National Comprehensive Cancer Network, and the St Gallen Consensus Conference,account for these factors in their recommendations, despite their absence from the TNMsystem.