Objective <p>To evaluate the efficacy of supraclavicular involved lymph node dissection combined with radiotherapy compared to radiotherapy alone in breast cancer patients with synchronous ipsilateral supraclavicular lymph node metastasis (sISLM).</p> Method <p>The clinical data of 326 breast cancer patients with sISLM admitted to the Fourth Hospital of Hebei Medical University from January 2010 to December 2021 were retrospectively analyzed. Patients were divided into two groups based on different local treatment patterns for sISLM: 88 cases (27.0%) in supraclavicular surgery plus radiotherapy group and 238 cases (73.0%) in radiotherapy alone group. 1:2 propensity score matching (PSM) was used to balance intergroup differences, resulting in 83 patients in the surgery plus RT group and 162 patients in the radiotherapy alone group. The Kaplan-Meier method and multivariate Cox proportional hazards model were employed to calculate the Localregion relapse-free survival (LRFS), supraclavicular recurrence-free survival (SCRFS), and overall survival (OS) for both groups.</p> Result <p>The median follow-up duration in the study was 67 months (Q1: 44, Q3: 94). No statistically significant differences were observed between the surgery combined with radiotherapy group and the radiotherapy alone group in terms of age, menstrual status, tumor location, hormone receptor status, molecular subtype, and clinical stage.Univariate survival analysis indicated that, the 5-year and 8-year survival for the surgery plus radiotherapy group and the radiotherapy alone group were 84.5%, 78.0%, 88.3% and 86.0%, respectively (<i>P </i>= 0.191). The SCRFS were 88.2%, 83.7%, 94.7% and 92.3%, respectively (<i>P </i>= 0.062). The OS were 67.0%, 58.8%, 75.1% and 63.9%, respectively (<i>P </i>= 0.564). Multivariate survival analysis revealed that Ki67＞30% were independent prognostic factors for poor LRFS(P = 0.032) and SCRFS(P = 0.026). Treatment period from 2010 to 2016, Hormone receptor positive/endocrine therapy negative(HR+/ET-), HR- and the ratio of involved axillary lymph node (ALNR) were independent prognostic factors for poor OS(all P ＜0.05). Subgroup analysis revealed that, irrespective of whether the supraclavicular lymph nodes achieved complete remission (CR) following neoadjuvant chemotherapy, there was no significant difference in prognosis between the two groups (<i>P</i> &gt;0.05). Among patients who received radiotherapy alone, those treated with 50-60Gy to the supraclavicular region exhibited superior 5-year and 8-year LRFS and SCRFS compared to those &gt;60Gy (<i>P</i> = 0.049, <i>P</i> = 0.034, respectively). Notably, in patients with non-CR supraclavicular involved lymph nodes, the 5-year and 8-year LRFS was significantly better in the 50-60 Gy group than &gt;60 Gy (<i>P</i> = 0.015).</p> Conclusion <p>Both radiotherapy alone and supraclavicular surgery combined with radiotherapy were considered local treatment strategies for patients with sISLM breast cancer involving supraclavicular lymph nodes. Within the framework of contemporary treatment, the exploration of lower-dose radiation for supraclavicular lymph nodes will proceed, irrespective of whether CR was achieved following neoadjuvant chemotherapy.</p>