Utilization of a Lumpectomy Bed Boost After Whole Breast Radiotherapy and Ipsilateral Breast Tumor Recurrence Risk in Patients With Ductal Carcinoma In-Situ Treated on Three NSABP Trials

Document Type

Conference Proceeding

Publication Date

9-2025

Publication Title

International Journal of Radiation Oncology, Biology, Physics

Abstract

Purpose/Objective(s): The seminal studies of adjuvant therapies in patients with ductal carcinoma in-situ (DCIS) did not routinely mandate or prohibit use of a lumpectomy bed boost after whole breast radiotherapy (RT). Delivery of this additional RT improves in-breast recurrence risk in invasive breast cancer patients. A recent trial demonstrated lower recurrence risk with boost in DCIS patients with adverse risk features. We studied the effect of boost utilization in women with DCIS treated on NRG trials. Materials/Methods: We examined data from three NSABP (now NRG) trials (B-24, B-35, and B-43), which exclusively studied women with DCIS. The primary endpoint of this cross-protocol study was time to ipsilateral breast tumor recurrence (IBTR, invasive or in situ), censored by regional/ distant recurrence, ipsilateral mastectomy, and either death or date of last mammogram, whichever came first. Stratified log-rank test was used to test whether boost reduced patients’ risk of IBTR, vs patients without boost. Stratification factors included study and potential study-specific confounders. Study-specific propensity score models were developed to predict boost status and were subsequently used in the inverse probability-weighted Cox model to assess effect of boost on risk of IBTR within each study. Then those results were summarized using random-effects meta-analysis. Results: A total of 6,922 randomized patients with follow-up data were included: 1,804 from B-24, 3,104 from B-35, and 2,014 from B-43. Use of boost was less frequent in B-24 (38.2%) vs B-35 (82.5%) and B-43 (83.4%). IBTR was more prevalent in B-24 (14.9%) than B-35 (2.3%) or B-43 (6.5%). Prevalence of IBTR was also balanced between the no-boost and boost groups: 15.1% vs 14.6% in B-24, 1.4% vs 2.5% in B-35, and 6.8% vs 6.4% in B-43. There was no evidence of an effect of boost on the risk of IBTR in the stratified log-rank test (p=0.9) or risk of recurrence (p=0.89). Meta-analysis did not reveal any effect of boost on the risk of IBTR (p=0.31). Conclusion: In this retrospective cohort study re-examining the correlation of boost utilization with IBTR risk, we did not find an association of boost with recurrence. We demonstrate a decreasing rate of IBTR over time and low overall rates of recurrence in boost and nonboost patients. This study represents the largest examination to date of the effect of boost on IBTR risk in DCIS. Important limitations include inconsistent use of boost within and across studies, heterogeneity of patients/treatment, non-standard definitions of boost volume/doses, and lack of pre-specified RT QA. Although these data do not definitely exclude benefit of boost in good-risk DCIS patients, the likelihood of a demonstrable benefit in patients at the low end of the risk spectrum appears to be low.

Volume

123

Issue

1 Suppl

First Page

S124

Last Page

S125

Comments

American Society for Radiation Oncology ASTRO 2025: 67th Annual Meeting, September 27 - October 1, 2025, San Francisco, CA

DOI

10.1016/j.ijrobp.2025.06.1190

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