Main Session
Sep
29
QP 25 - Clinical Potpourri: Navigating Early-Stage RT, N1mi Disease, and Risk Mitigation in Triple Negative and HER2+ Breast Cancer
1146 - Adjuvant Endocrine Therapy Adherence and Outcomes in Early Breast Cancer Patients Treated With APBI: A Retrospective Analysis Stratified by LUMINA Criteria
Presenter(s)
John Wilson V, BS - University of South Florida, Tampa, FL
J. D. Wilson V1, J. Redding1, G. Luckey1, R. H. Nanda Jr2,3, K. A. Ahmed2, L. Stout3, P. Blumencranz3, M. N. Mills2, and R. Diaz2; 1University of South Florida, Morsani College of Medicine, Tampa, FL, 2Department of Radiation Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, FL, 3Morton Plant Hospital, Clearwater, FL
Purpose/Objective(s):
Recent trials (e.g., CALGB-9343, PRIME II, LUMINA, IDEA, DEBRA) support omitting radiotherapy (RT) in select post-menopausal women with early breast cancer, relying on endocrine therapy (ET) alone post-lumpectomy. However, NSABP-B21 showed RT superior to ET for ipsilateral breast tumor recurrence (IBTR), and NCDB analyses in women aged 70 years or older indicate no 5-year overall survival difference between RT and ET monotherapies. ET has significant side effects and variable compliance, while ultra-hypofractionated RT/APBI is safe and convenient. We evaluated IBTR and other recurrence outcomes in post-menopausal breast cancer patients meeting RT-omission criteria but treated with APBI, stratified by endocrine therapy compliance, to assess potential for ET de-escalation.Materials/Methods:
Retrospective review of post-menopausal patients with early-stage invasive breast cancer treated with lumpectomy + SLNB + HDR brachytherapy APBI (34 Gy/10 fx BID, 2010-2022) at a single community center. Subsets meeting LUMINA criteria (age =55 y, T1N0, grade 1-2, luminal A surrogate: ER=1%, PR>20%, HER2-, Ki67=13.25%; n=131) and non-eligible (n=499) were stratified by ET duration: APBI only/short ET (=91 d) vs. APBI + long ET (=1795 d, ~5 y). Patients with ER/PR <1% were excluded from ET compliance analysis (n=45). Primary outcome: IBTR. Secondary: contralateral breast tumor recurrence (CBTR), regional recurrence (RR), distant recurrence (DR). Kaplan-Meier and log-rank tests were used.Results:
Median follow-up was 95.9 months (8.0 years) (range 1.6–189 months). Crude recurrence rates are shown below: Among LUMINA-eligible patients, 5- and 10-year IBTR were 0% and 0% with =91 days ET versus 2.3% and 2.3% with long ET (p=0.355). Among non-eligible patients, 5- and 10-year IBTR were 8.8% and 23.9% versus 0% and 3.5% with long ET (p<0.001). Sensitivity analysis of short endocrine adherence extended to =1 year showed IBTR of 4.3% (2/46), still comparable to long ET. No significant differences in CBTR, RR, or DR within strata.Conclusion:
In LUMINA-eligible patients treated with APBI, adjuvant endocrine therapy provided no meaningful benefit (0% IBTR with short/no ET =3 months vs. 4.5% with long ET). In non-eligible patients, long ET significantly reduced IBTR (17.6% vs. 3.9%, p<0.01). These results support de-escalation of ET in low-risk cases and continued use in higher-risk disease, challenging reliance on long-term endocrine therapy in all ER+ patients amid its toxicities and supporting prospective trials (e.g., maturing EUROPA) to evaluate ET omission in the ultra-hypofractionated RT/APBI era for select low-risk patients.| Group | n | IBTR (%) | CBTR (%) | RR (%) | DR (%) |
| LUMINA Met + APBI Only (= 91 d ET) | 30 | 0.0 | 3.3 | 0.0 | 0.0 |
| LUMINA Met + APBI + Long ET | 44 | 4.5 | 4.5 | 2.3 | 2.3 |
| LUMINA Not Met + APBI Only (= 91 d ET) | 85 | 17.6 | 8.2 | 4.7 | 3.5 |
| LUMINA Not Met + APBI + Long ET | 204 | 3.9 | 6.4 | 3.4 | 2.5 |