Rethinking tumour bed boost irradiation after pathological complete response in breast cancer

Tumour bed boost irradiation has long represented a cornerstone of breast-conserving treatment, improving local control at the cost of increased fibrosis, poorer cosmetic outcomes, and reduced quality of life. However, the landscape of early breast cancer has changed profoundly. Modern systemic therapies and the widespread adoption of neoadjuvant treatment have made pathological complete response (pCR) an increasingly common and clinically meaningful endpoint, consistently associated with excellent long-term outcomes.Despite this biological revolution, local treatment strategies remain largely unchanged and continue to follow standards developed in the pre-neoadjuvant era. Yet, pCR likely reflects not only treatment efficacy but also favourable tumour biology and intrinsic radiosensitivity, raising the question of whether all patients who achieve pCR still derive a meaningful incremental benefit from routine tumour bed boost irradiation. As survivorship becomes an increasingly important outcome, minimizing treatment-related toxicity without compromising local control is a major priority. Prospective trials evaluating response-adapted boost strategies are therefore urgently needed. Radiotherapy should evolve alongside systemic therapy, moving from a 'one-size-fits-all' approach toward truly biology-driven personalization.