Prognostic relevance of biological subtype overrides that of TNM staging in breast cancer: discordance between stage and biology.

Recently, we faced difficult treatment decisions regarding appropriate adjuvant systemic treatment, especially for patients who show discordance between stage and tumor biology. The aim of this study was to compare the prognostic relevance of the TNM staging system with that of intrinsic subtype in breast cancer. We retrospectively identified women patients who received curative surgery for stage I-III breast cancer with available data on immunohistochemistry profiles including hormone receptor (HR) status, human epidermal growth factor receptor 2 (HER2) status, and Ki 67 staining at the Samsung Medical Center from January 2004 to September 2008. Primary outcomes were recurrence-free survival (RFS) and overall survival (OS). A total of 1145 patients were diagnosed with breast cancer and received curative surgery. Of these, 463 (40.4%) patients were stage I, and 682 (59.6%) were stage II or III. In addition, 701 (61.2%) patients were HR positive, 239 (20.9%) were HER2 positive, and 205 (20.9%) had triple-negative breast cancer. The 5-year RFS for the patients who were HR positive and HER2 negative with a low Ki 67 staining score (0-25%) was 99%. The 5-year RFS for patients who were HER2-positive or had triple-negative breast cancer were 89 and 83%, respectively (P value = <0.001). In multivariate analysis, advanced stage (II/III) and unfavorable biology (HER2 positive or triple negative) retained their statistical significance as predictors of decreased RFS and OS. Patients with advanced-stage disease (II or III) but favorable tumor biology (HR positive and HER2 negative and low Ki 67) had better clinical outcomes than those with stage I disease and unfavorable tumor biology in terms of RFS (99 versus 92%, P value = 0.011) and OS (99 versus 96%, P value = 0.03) at 5 years. The current results showed that intrinsic subtype has a greater prognostic impact in predicting clinical outcomes in subpopulations of patients with stage I-III breast cancer who show discordance between stage and biologic subtypes.