The Tumor-Bed Boost Irradiation in Early-Stage Breast Cancer 30 Years After the Landmark Trials: What Is New?

Breast-conserving surgery followed by adjuvant whole-breast irradiation (WBI) remains the standard of care for patients with early-stage breast cancer. In this setting, irradiation of the tumor bed with an additional boost dose has historically been used to reduce the risk of ipsilateral breast tumor recurrence (IBTR). Major randomized trials established that boost irradiation improved local control, particularly in younger patients, but did not confer a consistent overall survival (OS) benefit and was associated with increased late toxicity, like fibrosis, and poorer cosmetic outcomes as well. More recent evidence, including systematic reviews and contemporary consensus recommendations, suggests that boost irradiation may be safely omitted in selected low-risk patients, especially when the estimated absolute reduction in 10-year local recurrence is less than 3%. At the same time, the routine use of boost irradiation has been challenged by modern systemic therapy treatments questioning if boost could be really omitted in this set. Further advances in radiation techniques are redefining the scheduling and timing of boost administration, shifting from a conventional fractionation to hypofractionation and from the sequential (SEB) to simultaneous delivery with simultaneous integrated boost (SIB). In light of increasingly minimally invasive surgery and a de-escalation RT policy, unresolved clinical issues still remain about the management of positive or close margins and the role of boost irradiation in ductal carcinoma in situ. This narrative review summarizes the biological rationale, historical trial evidence, and recent literature addressing these evolving scenarios. Current evidence supports a more individualized approach to boost prescription based on recurrence risk, patient age, tumor biology, margin status, treatment techniques (surgery and radiotherapy), and patient preference.