Long-term cosmetic changes after breast-conserving treatment of patients with stage I-II breast cancer and included in the EORTC 'boost versus no boost' trial

In breast cancer treated with breast-conserving radiotherapy, the influence of the boost dose on cosmetic outcome after long-term follow-up is unknown. We included 348 patients participating in the EORTC 'boost versus no boost' mega trial with a minimum follow-up of 6 years. Digitalised pictures were analysed using specific software, enabling quantification of seven relative asymmetry features associated with different aspects of fibrosis. After 3 years, we noted a statistically significantly poorer outcome for the boost patients for six features compared with those of the no boost patients. Up to 9 years of follow-up, results continued to worsen in the same magnitude for the both patient groups. We noted the following determinants for poorer outcome: (i) boost treatment, (ii) larger excision volumes, (iii) younger age, (iv) tumours located in the central lower quadrants of the breast and (v) a boost dose administered with photons. A boost dose worsens the change in breast appearance in the first 3 years. Moreover, the development of fibrosis associated with whole-breast irradiation, as estimated with the relative asymmetry features, is an ongoing process until (at least) 9 years after irradiation.