Abstract： Objective To analyze the role of 21-gene detection in postoperative adjuvant chemotherapy for ER-positive early breast cancer.Methods Selected from April 2020 to April 2022,Ninety female patients who re-ceived breast cancer surgery in our hospital were selected.The patients were ER positive and lymph node neg ative in postoperative pathological examination,and immunohistochemical method was used to detect cell nu-clei.Related antigen(Ki-67)and estrogen receptor(ER)expression;21 genes were detected by branched DNA-liquid phase chip technology.Results After performing the 21-gene detection recurrence risk score for breast cancer patients,90 patients were divided into 63 low-risk patients and 27 medium-and high-risk pa-tients.There were significant differences between TNM staging,clinical staging,molecular typing,Ki-67 posi-tive index,ER positive index and 21-gene detection(P＜0.05).Before the 21-gene test,37 patients were pre-liminarily determined to be suitable for adjuvant endocrine therapy(HT)program,including 34 patients with low risk and 3 patients with medium and high risk.53 patients were suitable for adjuvant chemotherapy+en-docrine therapy(CHT)program,of which 29 were low-risk patients and 24 were medium-high risk patients.Seventy-two patients were treated with the HT regimen,of which 35 patients were changed from the CHT regimen to the HT regimen,26 were low-risk patients,and 9 were intermediate-high risk patients.In contrast,18 patients underwent CHT,including 3 low-risk patients and 15 medium-high risk patients.There were no additional adjuvant chemotherapy patients for other breast cancer patients during this period.There was a sta-tistical difference between before and after the 21-gene detection(P＜0.05).Conclusion Using 21 genes to detect ER-positive early breast cancer patients,its recurrence risk score can significantly avoid excessive adju-vant chemotherapy after surgery for patients with different risks,thereby reducing the incidence of postopera-tive chemotherapy for these patients,thereby reducing the number of patients Side effects after self-chemo-therapy.