The article presents a comprehensive study on the gene expression profiling of breast cancer, aiming to predict clinical outcomes and identify prognostic markers. The authors used DNA microarray analysis to profile gene expression in 98 primary breast tumors, focusing on 5,000 significantly regulated genes. They identified two distinct tumor clusters based on unsupervised clustering, one with a higher risk of distant metastases and another with a lower risk. Supervised classification methods were then applied to select a set of 70 genes that strongly predict the short interval to distant metastases in lymph node-negative patients. This classifier outperforms current clinical parameters in predicting disease outcome. Additionally, the authors developed a two-layer classification system to distinguish between ER-positive and ER-negative tumors, and further divided ER-negative tumors into BRCA1 mutation and sporadic cases. The study highlights the potential of gene expression profiles to tailor adjuvant systemic therapy and improve patient outcomes.The article presents a comprehensive study on the gene expression profiling of breast cancer, aiming to predict clinical outcomes and identify prognostic markers. The authors used DNA microarray analysis to profile gene expression in 98 primary breast tumors, focusing on 5,000 significantly regulated genes. They identified two distinct tumor clusters based on unsupervised clustering, one with a higher risk of distant metastases and another with a lower risk. Supervised classification methods were then applied to select a set of 70 genes that strongly predict the short interval to distant metastases in lymph node-negative patients. This classifier outperforms current clinical parameters in predicting disease outcome. Additionally, the authors developed a two-layer classification system to distinguish between ER-positive and ER-negative tumors, and further divided ER-negative tumors into BRCA1 mutation and sporadic cases. The study highlights the potential of gene expression profiles to tailor adjuvant systemic therapy and improve patient outcomes.