Significance of boost radiotherapy in early invasive ductal breast cancer with ductal carcinoma in situ component under negative surgical margins

We hypothesize that there is a risk of ipsilateral breast tumor recurrence (IBTR) in surgical margin-free invasive ductal carcinoma (IDC) in the presence of ductal carcinoma in situ (DCIS) component affecting surgical margins in early stage. From 1990 to 2014, 343 patients with IDC in which the DCIS component constitute have received radiotherapy (RT) following breast-conserving surgery (BCS). All patients received whole breast irradiation with a prescribed dose of 50 Gy in 20 fractions (four times a week). This one-arm cohort with boost RT (253 patients) was compared for IBTR with a non-cohort group receiving no boost RT because of freedom from positive margins (90 patients). Median observation months were 98 (boost group) vs 119 (no boost group), respectively. The 15-year local recurrence-free survival (LRFS) rates were 98.5% and 85.6% in the boost and no boost groups, respectively (Cox proportional hazards model univariate analysis; p = 0.013, HR 0.13). Similarly, for other background factors, there was a significant difference in the LRFS between age groups. The 15-year LRFS rate was 91.8% in patients aged 45 years or younger and 94.6% in patients older than 46 years (p = 0.031, HR 0.21), respectively. Only these two factors were independently significant in Cox proportional hazards model multivariate analysis. IBTR risk in margin-free IDC with DCIS component was independently decreased by boost RT in the cohort setting. Tumor size, extensive intraductal component (EIC), boost dose, the presence of lymph node (LN) metastasis and hormonal therapy were not IBTR risk factors in this study.