In conclusion, in this real-life data analysis focusing on estrogen receptor (ER) + HER2‒ BC patients with RS 26–30, N0 patients with low-risk according to clinicopathologic characteristics were more likely to forego adjuvant CT, and their clinical outcomes (OS, DRFS, BCSM) with ET alone were excellent, and not statistically significantly different from those of N0 patients who did receive CT. The gene discussed is ESR1; the disease is breast cancer.