Park SJ, et al. - Researchers assessed the factors that changed trends in chemotherapy after the 21-gene expression assay in tumor genomic profiling for breast cancer was adopted. For this purpose, they evaluated patients from the National Cancer Center in Korea diagnosed with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer (tumor size of 0.5 cm or larger and 0–3 node metastases). They found that the adoption of the 21-gene assay resulted in a significant decline in the use of chemotherapy for HR-positive, HER2-negative breast cancer patients with 0–1 node metastases. In cases without the 21-gene assay, the utility of progesterone receptor status and proliferation index for chemotherapy decision-making was shown.