Abstract PD7-04: Avoidance of radiotherapy for low risk early breast cancer using LUMINA Trial criteria and accounting for endocrine therapy adherence
Authors: Seol Seung Won , Weller Lauren , Pflederer Travis , Goodman Chelain , Donnelly Eric D , Hayes John P , Strauss Jonathan B 
Published: March 2022

Objectives: Adjuvant radiotherapy (RT) is a standard component of breast conserving therapy for early stage breast cancer. However, in especially low risk disease, the benefit of radiotherapy may be small. Randomized trials have investigated the feasibility of RT omission in subgroups of patients defined by clinicopathologic variables only. Five biomarker based single arm trials (IDEA, PRECISION, LUMINA, PRIMETIME, EXPERT trials) are ongoing with the goal of using molecular data to refine patient selection for RT omission. This analysis reports on the treatment outcomes of low risk ER positive early stage breast cancer treated with adjuvant RT or RT omission at a multi-hospital health system. Inclusion criteria from LUMINA trial were used to select a very low risk population and subgroup analyses were performed to investigate the influence of endocrine therapy (ET) adherence on outcomes. Methods: The shared electronic health record of multiple facilities within a university health system was queried to identify women with pathologic T1-2 N0 breast cancer treated with breast-conserving surgery between 2007 and 2016. Data collection included demographic features, tumor characteristics, treatment type, endocrine therapy adherence, and locoregional recurrence events. Analysis was restricted to those patients treated with EBRT or RT omission. To identify the low risk patients, inclusion and exclusion criteria from LUMINA trial (age ≥ 55, unifocal, unilateral, ductal, tubular or mucinous histology, T1N0, grade 1-2, ER+ and PR&gt;20 and HER2-, LVI -, margin &gt; 2mm, Ki67 ≤ 13.25, agreed to start endocrine therapy) were applied. Five-year loco-regional control (LRC) rates were compared across groups using the Kaplan-Meier method. Results: 115 patients met LUMINA inclusion criteria. Of these, 84 were treated with EBRT and 31 with RT omission. ET adherence information were available for 101 patients. Patients who completed 5 years of ET or discontinued owing to disease recurrence or death were categorized as ET adherent (ETA) and those who discontinued before 5 years due to other reasons were categorized as ET non-adherent (ETNA). Median ET duration in ETA was 60 months (49-118 months) and in ETNA was 19 months (1-58 months). 5-year LRC rates for RT vs. RT omission were 100 % vs. 94 % (95% CI 82-100). This difference was borderline statistically significant (p = 0.06). On subset analysis, 5-year LRC rates for RT and RT omission were both 100 % in ETA. The 5-year LRC rates for RT vs. RT omission were 100 % vs. 83% (95% CI 54-100) in ETNA (p= 0.18). Conclusion: In this modern series, patients with very low risk early breast cancer selected using criteria from the LUMINA trial exhibited excellent local control with ET alone if they were treatment adherent. This finding awaits validation in large prospective cohorts. By contrast, ET alone may be insufficient in patients likely to be non-adherent to treatment. Notably, prospective trials should closely follow and report ET adherence.

Table 1.Patient tumor and treatment characteristicsEBRT (n=84)RT omission (n=31)Age (median)63 (55-76)73 (63-81)Median follow-up (months)53 (8-98)43 (7-70)HistologyDuctal72 (86%)30 (97%)Other12 (14%)1 (3%)StageT1mic2 (2%)0T1a12 (14%)9 (29%)T1b34 (41%)11 (35%)T1c36(43%)11 (35%)GradeG149 (58%)23 (74%)G235 (42%)8 (26%)Endocrine therapy (ET)ET median duration (months)60 (2-118)55 (1-72)ET Adherent60 (71%)17 (55%)ET Non-adherent15 (18%)9 (29%)ET adherence not available9 (11%)5 (16%)

Table 2.5-year Loco-regional control ratesRTRT omissionLog-rank test p valueLUMINA All (N=115)100%94%0.06LUMINA ET Adherent (N=77)100%100%LUMINA ET Non-adherent (N=24)100%83%0.18

Citation Format: Seung Won Seol, Lauren Weller, Travis Pflederer, Chelain Goodman, Eric D Donnelly, John P Hayes, Jonathan B Strauss. Avoidance of radiotherapy for low risk early breast cancer using LUMINA Trial criteria and accounting for endocrine therapy adherence [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD7-04.