The standard model of breast-conserving treatment for early-stage breast cancer is breast-conserving surgery, postoperative radiotherapy, and adjuvant systemic therapy after surgery. Currently, most early invasive breast cancers require 45-50 Gy of postoperative whole-breast radiotherapy (+/- tumor bed plus 10-16 Gy) after breast-conserving surgery; however, two recent studies have shown that a subset of patients with very low risk of local recurrence can be treated with endocrine therapy alone after breast-conserving surgery, omitting radiotherapy. The first study was designed by CALGB in collaboration with ECOG and RTOG and is also known as the C9343 study. The results of this study were published in the New England Journal in 2004.The main criteria for patient enrollment in the C9343 study were: age ≥70y; clinical stage T1N0M0; ER+ or status unknown. Eligible patients underwent breast-conserving surgery and were then randomized to TAM alone and TAM+RT; the radiotherapy regimen was an ipsilateral total mastectomy of 45GY/25F; and study endpoints included LR. A total of 636 patients were enrolled. There were no significant differences between the two groups in terms of OS, distant metastases, or the proportion of patients who underwent mastectomy for local recurrence, with the only statistically significant difference being the 5-year local-regional recurrence rate (1% in the control group vs. 4% in the trial group). Although the recurrence rate was slightly higher in patients without radiotherapy, it was still within 5%, and the proportion of mastectomies for recurrence did not increase, nor were distant metastases and OS affected. This shows that the benefit of radiotherapy patients is limited. Therefore, the significance of the C9343 study is that it helped us to find a group with a very low risk of local recurrence, characterized by age 70 or older, a mass less than 2 cm, and positive ER. For patients who fit these characteristics, TAM therapy alone after breast-conserving surgery, omitting radiotherapy, is a realistic option. The second is the PRIME trial, a phase III clinical study designed to evaluate the value of radiotherapy after breast-conserving surgery in patients with very low-risk breast cancer. In the PRIME study, patient enrollment criteria included age 65 years or older, negative margins after breast-conserving surgery, masses up to 3 cm, negative lymph nodes, and ER+/PR+. Patients who met the enrollment criteria were randomized to receive whole breast radiotherapy + endocrine therapy in the control group and endocrine therapy alone in the trial group. The primary study endpoint was the ipsilateral intramammary recurrence rate (IBTR); secondary endpoints included regional recurrence (RR), etc. A total of 1326 patients were enrolled from 2003 to 2009, with a median follow-up of 4.8 years. The 5-year IBTR was 4.1% and 1.3% for the trial and control groups, respectively, with a statistically significant difference of 3.2% and 0.8% for patients with an ER score of 7 or higher. However, it is questionable how clinically significant this difference actually is. For example, for every 100 patients eligible for enrollment and treated with radiotherapy, although 3 recurrences were avoided, 1 patient would still recur and radiotherapy would be meaningless in another 96 patients, so >95% of patients received unnecessary irradiation. In terms of secondary endpoints, there was no statistical difference in all endpoints except cancer-free survival, which improved from 96.4% to 98.5%, mainly attributed to a reduction in IBTR. In this way, this study also helped us to find a subgroup of patients with very low risk of recurrence, defined as: age 65 years or older, mass less than 3 cm, negative lymph nodes, and ER/PR+. For this subgroup, omitting radiotherapy and giving only endocrine therapy is a reasonable option. These two studies tell us that a subset of breast cancer patients treated with breast-conserving therapy have a low risk of local recurrence, so low that they do not need the intervention of radiotherapy and only endocrine therapy should be given. Therefore, the view that radiotherapy is necessary after breast-conserving surgery for early-stage breast cancer needs to be gradually changed.