ABSTRACT

Background. Clinical trial data support the omission of radiation therapy (RT) in older women with early-stage
breast cancer. The majority of older women still receive RT largely due to a lack of insight regarding endocrine therapy
(ET) tolerance. The POWER trial is a phase II trial designed to determine whether 90 days of preoperative ET (pre-ET)
changes patient or surgeon preferences for RT.
Methods. Between 2020 and 2024, two centers enrolled women aged 65 years or older with invasive carcinoma measuring ≤2 cm, N0, and ER+/PR±/HER2−. All participants were recommended for 90 days of pre-ET. Patient and
surgeon preferences for RT were evaluated before and after pre-ET. A change in preference was tested from an assumed
low change rate of 5% to a rate of ≥15%, with a one-sided 5% level binomial test.
Results. Seventy-five women enrolled. Adverse events attributed to pre-ET occurred in 35 participants (47%). After
pre-ET, 21 (28.0%) patients changed RT preference and surgeons changed RT recommendation for 18 (24.0%) patients
(p < 0.001 and p = 0.015, respectively). General agreement between patient and surgeon preferences before pre-ET was
53% (Kappa = −0.04) and increased to 81% (Kappa = 0.59) after pre-ET.
Conclusion. Pre-ET significantly changed patient and surgeon preferences for RT and increased patient and surgeon
agreement. The intentional resequencing of treatments enables patients to assess tolerance to ET before deciding whether to omit RT. This study validates pre-ET as a innovative method to inform adjuvant therapy decisions and
recommendations.