Response to Neoadjuvant Systemic Therapy May Serve as an Indicator for Omitting Post-Breast-Conserving Surgery Radiation Therapy in Women with Early-Stage Breast Cancer.

Purpose: To avoid unnecessary toxicities and optimize the allocation of healthcare resources, it is crucial to adequately select patients with extremely low recurrence risk to downgrade or eliminate radiation therapy (RT). Materials and Methods: From the Surveillance, Epidemiology, and End Results database, clinical data of 7,291 female patients with early-stage breast cancer who underwent neoadjuvant systemic therapy (NST) and breast-conserving surgery (BCS) were collected for this study. The patients were stratified by their response to NST, and the long-term survival and risk of recurrence were assessed using Cox regression analysis and Fine-Gray competing risk models for those with and without post-BCS RT, respectively. Results: Our results showed that female patients with early-stage breast cancer who achieved complete response (CR) to NST, omitting post-BCS RT achieved the same overall survival and disease-free survival as those who received the post-BCS RT, and the omission did not increase the risk of recurrence or breast cancer-specific death. For patients who did not achieve CR to NST, five clinical indicators (including age, N category, grade, response to NST, and molecular subtype) were employed to construct a nomogram for clinical prediction of overall survival, thereby identifying of patients at relatively low recurrence risk. The validated results affirmed our model's ability to accurately discriminate high- and low-risk patients and its promising clinical application value. Conclusion: Post-BCS RT can be omitted for women with early-stage breast cancer who achieved CR to NST. For those who failed to achieve CR to NST, a nomogram was constructed for clinicians to decide whether to omit post-BCS RT or not based on individualized assessment.