Following breast conserving surgery, the risk of ipsilateral in-breast recurrence is equivalent between whole breast radiation therapy (WBRT) and accelerated partial breast irradiation (APBI) in patients with low-risk tumors according to ASTRO guidelines. The Oncotype DX Recurrence Score (RS) is prognostic for both local and distant recurrence in ER+/HER2-breast cancer. Whether the RS can identify patients at increased risk for local recurrence among those considered eligible for APBI is unclear. Materials/Methods: We retrospectively identified consecutive patients with clinical T1-2, ER+/HER2-, node-negative tumors with an available RS, and who were treated with APBI from 2010-2019 at a single institution. RS testing was performed for all patients with ER+/HER2-, invasive cancers ≥ 0.5 cm who were candidates for chemotherapy. Patients were considered for APBI based on the 2009 ASTRO guidelines. Characteristics were compared between patients with RS ≤ 25 and RS > 25 using Fisher's exact test for categorical variables and the Wilcoxon rank sum test for continuous variables. The 6-year cumulative incidence rate (CIR) of local recurrence was estimated using Kaplan-Meier methods and was compared between groups using the log-rank test. Results: 223 patients were identified; the median (IQR) age was 63 years (57-68) and median (IQR) tumor size was 1.0 cm (0.8-1.4). 201 patients (90%) had RS ≤ 25 and 22 patients (10%) had RS > 25. Nine patients aged ≤ 50 years were included, all of whom had RS ≤ 25. Compared with the RS ≤ 25 group, patients with RS > 25 more frequently had tumors that were progesterone receptor negative (55% vs. 9%; P < 0.001), grade III (50% vs. 11%; P < 0.001) and were more likely to have received chemotherapy (73% vs. 5%; P < 0.001). Uptake of endocrine therapy was similar in the RS ≤ 25 group compared with RS > 25 group (97% vs. 95%; P = 0.39), as was median (IQR) duration of endocrine therapy at 3 years (2-5) for both groups (P = 0.9). The median (range) follow-up was 3.6 years (0.1-10.2) and was similar between groups (P = 0.64). Overall, 4 ipsilateral in-breast recurrences occurred during follow-up, with 2 events (1.0%) in the RS ≤ 25 group and 2 events (9.1%) in the RS > 25 group (P = 0.05). The 6-year CIR of local recurrence was higher among patients with RS > 25 compared with RS ≤ 25 (6-year CIR [95%
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.