Prevention of locoregional recurrence and distant metastasis in Japanese breast cancer patients using Japanese standard postoperative radiation fields: Experience at a single institution

BACKGROUND Radiotherapy is an effective local control therapy for breast cancer. Locoregional control is associated with distant metastasis risk and survival after surgery. AIM We aimed to evaluate whether Japanese standard postoperative radiotherapy after surgery correlates with disease-free survival (DFS) and overall survival and clarify the characteristics of patients who benefit from it. METHOD AND RESULTS This retrospective study included 626 operable breast cancer patients. Tumor characteristics and survival outcomes were compared between patients who received radiotherapy and those who did not. Cox proportional hazard analysis was used to analyze prognostic factors for DFS and perform subgroup analysis. Propensity score matching was used to evaluate the efficacy of radiotherapy using a logistic regression model in patients who received radiotherapy or did not. The median follow-up duration after diagnosis of breast cancer was 63 months. DFS and overall survival were better in the irradiated group (P= .002 and P = .001, respectively). Radiotherapy was more effective for estrogen receptor (ER)-positive disease and for early breast cancer without lymph node metastasis. Multivariate analysis revealed that radiotherapy was a dependent risk factor for recurrence or metastasis. CONCLUSION Radiotherapy prevents distant metastasis and recurrence in early breast cancer patients. In particular, ER-positive, node-negative patients benefit from Japanese standard tangent field radiation.