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

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.

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.

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.

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.