Is Tumor Bed Boost Necessary in Young Patients With Margin-negative Invasive Ductal Carcinoma in the Modern Radiotherapy Era?

BACKGROUND/AIM: To evaluate whether tumor-bed boost irradiation improves local control outcomes in women aged 50 years or younger with invasive ductal carcinoma (IDC) and widely negative margins after breast-conserving surgery (BCS), and to clarify its clinical value within a modern, risk-adapted radiotherapy strategy. PATIENTS AND METHODS: This retrospective single-center study included 318 female patients aged ≤50 years with IDC and negative surgical margins (>5 mm) who underwent BCS followed by whole-breast irradiation (WBI) at Tohoku University Hospital between 2008 and 2022. Patients treated before 2016 did not receive boost irradiation, whereas those treated thereafter received a 10 Gy tumor-bed boost. Survival estimates were calculated using the Kaplan-Meier method from the first date of radiotherapy. RESULTS: Among the 318 eligible patients, 110 received boost irradiation and 208 did not. Luminal disease was the predominant subtype in both groups (87/110 in the boost group and 159/208 in the non-boost group), whereas triple-negative disease was uncommon (11/110 and 18/208, respectively). After a median follow-up of 95.5 months, the 7-year ipsilateral breast tumor recurrence (IBTR) rates were 1.2% and 0% (log-rank p=0.859), while the 7-year overall survival (OS) rates were 97.9% in the non-boost group and 96.6% in the boost group (log-rank p=0.616), respectively. There were no significant differences in IBTR or OS between groups. CONCLUSION: In female patients aged ≤50 years with IDC and widely negative surgical margins following BCS, the addition of a 10 Gy tumor-bed boost did not demonstrate a significant improvement in IBTR or OS. These findings suggest that routine boost irradiation may not be necessary in carefully selected low-risk patients and support a risk-adapted approach to postoperative radiotherapy.