Locoregional Control Benefit of a Tumor Bed Boost for Ductal Carcinoma In Situ (DCIS)

Radiotherapy (RT) following breast conserving surgery (BCS) for ductal carcinoma in situ (DCIS) reduces invasive and in situ recurrences. Whereas landmark studies suggest that a tumor bed boost improves local control for invasive breast cancer, the benefit in DCIS remains less certain. We evaluated outcomes of DCIS patients treated with or without a boost and hypothesized that a tumor bed boost would improve locoregional control rates.The study cohort comprised patients with DCIS who underwent BCS at our institution from 2004-2018. Clinicopathologic features, treatment parameters and outcomes were ascertained from medical records. Patient and tumor characteristics were evaluated relative to outcomes using univariable and multivariable Cox models. Recurrence-free survival (RFS) estimates were generated using the Kaplan Meier method.We identified 1675 patients who underwent BCS for DCIS (median age 56 [interquartile range (IQR) 49, 64]). Boost RT was employed in 68% of cases (n = 1146) and endocrine therapy in 32% (n = 536). At a median follow-up of 4.2 years (IQR 1.4, 7.0), we observed 61 locoregional recurrence events (56 local, 5 regional) and 21 deaths. Univariable logistic regression demonstrated that boost RT was more common among younger patients (p<0.001) with positive/close margins (p<0.001), and with larger tumors (p<0.001) of higher grade (p = 0.025). The 10-year RFS rate was 88.8% among those receiving a boost and 84.3% among those without a boost (p = 0.3), and neither univariable nor multivariable analyses revealed an association between boost RT and locoregional recurrence.Among patients with DCIS who underwent BCS, use of a tumor bed boost was not associated with locoregional recurrence or RFS. Despite a preponderance of adverse features among the boost cohort, outcomes were similar to those not receiving a boost, suggesting that a boost may mitigate risk of recurrence among patients with high-risk features. Ongoing studies will elucidate the extent to which a tumor bed boost influences disease control rates.