Radiotherapy With a 12-Gene Expression Assay for Ductal Carcinoma In Situ

Importance Breast ductal carcinoma in situ (DCIS) requires personalized treatment given its variable natural history. This study reports the first prospective oncologic outcomes of radiotherapy decisions as guided by 12-gene molecular assay, the DCIS score (DS). Objective To assess surgical outcomes following preoperative breast magnetic resonance imaging (MRI) in women with DCIS and estimate 5-year and 10-year ipsilateral breast event (IBE) rates in participants given DS-based postoperative radiotherapy recommendations after local excision (WLE). Design, Setting, and Participants Women with screen-detected DCIS who were eligible for WLE were enrolled to a single-arm, multicenter trial conducted at 75 institutions within the Eastern Cooperative Oncology Group–American College of Radiology Imaging Network (March 2015 to April 2016) and received a preoperative breast MRI-guided surgical treatment. Those who underwent successful WLE were advised to omit radiotherapy for low DS (lt;39) and receive radiotherapy for intermediate/high DS (≥39). Those achieving WLE as final treatment and successful DS assay (n = 171) were included in a prespecified analysis. Participants were followed up every 6 months for DCIS or invasive IBE, and 5-year IBE rates were analyzed from July to November 2023. Intervention DS-based postoperative radiotherapy recommendations. Main Outcomes and Measures Five-year IBE rates, with 95% CIs. Results Among the 339 participants, the mean (SD) age was 59.1 (10.1) years. A total of 171 women (50.4%) received WLE for pure DCIS with free surgical margins and had DS data available. A total of 159 (93.0%) adhered to DS-based radiotherapy recommendations; 7 of 82 patients (8.5%) with a low DS underwent radiotherapy, and 5 of 89 patients (5.6%) with an intermediate/high DS declined radiotherapy. Over median (range) follow-up of 5 (0.5-5.0) years, 8 of 171 women experienced IBEs (4.8%; 95% CI, 2.4%-9.4%). IBE rates were similar for participants with a low DS(5.1%; 95% CI, 1.9%-12.9%) and participants with an intermediate/high DS (4.5%; 95% CI, 1.7%-11.7%). Among the 159 women who had adhered to DS-based radiotherapy recommendations, IBE rates were similar for participants with a low DS (5.5%; 95% CI, 2.1%-14.1%) and intermediate/high DS (4.8%; 95% CI, 1.8%-12.3%). Conclusions and Relevance The findings of this prespecified analysis of a clinical trial suggest that DS-guided radiotherapy post-WLE for DCIS shows markedly lower 5-year IBE rates (approximately 5%) for intermediate/high DS than previously reported data following WLE alone. Despite a limited sample size, these data potentially provide support for radiotherapy use in patients with intermediate/high DS, and omission when DS is low, although confirmatory studies are needed. Trial Registration ClinicalTrials.gov Identifier: NCT02352883