Established and new horizons in radiotherapy for breast cancer.

Modern advances in diagnostics, surgery, systemic therapies, and radiotherapy (RT) have drastically revolutionized treatment strategies for breast cancer. This review outlines current and evolving treatment paradigms for RT in the breast-conserving therapy and post-mastectomy setting. In early-stage breast cancer, there is active investigation in expanding eligibility for omission of RT in women with more biologically favorable tumors and growing options to effectively irradiate less breast tissue and shorten RT treatment courses. For locally advanced breast cancer, we discuss several patient cohorts in which the necessity of post-mastectomy RT (PMRT) is commonly debated. Ongoing efforts to better refine indications for PMRT and evaluate the feasibility of hypofractionated PMRT are being studied. Metastasis-directed therapy with ablative RT is an emerging topic of interest in many cancers, including its role and impact in oligometastatic breast cancer. In this review, we will discuss the rationale for current standard of care and address in greater detail the aforementioned concepts.