Locoregional Treatment of the Primary Tumor in Patients With De Novo Stage IV Breast Cancer: A Radiation Oncologist's Perspective

De novo stage IV breast cancer, a disease that is metastatic from the start, is relatively uncommon. The survival rate varies considerably, but most patients receive only systemic therapy. The efficacy of locoregional treatment like surgery and/or radiotherapy is controversial. We retrospectively assessed the benefits of locoregional treatment of the primary site in de novo stage IV breast cancer. Background: The aim of this study was to assess the outcomes of patients with de novo stage IV breast cancer after locoregional treatment (LRT) of primary site. Patients and Methods: We studied 245 patients diagnosed with de novo stage IV breast cancer. LRT of the primary tumor (+ systemic therapy) was performed in 82 (34%) patients (surgery, 27; surgery + radiotherapy (RT), 46; and RT, 9). Among those undergoing surgery, 64 (88%) patients underwent mastectomy, and 9 (12%) patients underwent breast-conserving surgery (BCS). Local recurrence-free survival (LRFS) and overall survival (OS) were investigated, and propensity score matching was used to balance patient distributions. Results: The 5-year LRFS and OS rates were 27% and 50%, respectively. Advanced T stage (T4), liver or brain metastasis, ≥ 5 metastatic sites, and absence of hormone therapy were significant adverse factors for LRFS, whereas T4 stage and absence of hormone therapy were significant for OS. The LRT group demonstrated significantly more favorable outcomes (5-year LRFS, 61%; 5-year OS, 71%), especially after surgery. After matching, survival rates remained significantly higher for patients who received LRT (5-year LRFS, 62% vs. 20%; P <.001; 5-year OS, 73% vs. 45%; P =.02). BCS + RT was superior to mastectomy ± RT, which can be attributed to more patients with a low tumor burden undergoing BCS + RT. Outcomes were better with post-mastectomy RT in selected patients (≥ N2, ≥ T3, or T2N1). Conclusions: Upfront LRT including RT is an important option together with systemic therapies for de novo stage IV breast cancer.