Providing a brief, 90-day course of preoperative endocrine therapy to older women with early-stage, estrogen receptor–positive, invasive breast cancer may significantly alter both patient preferences and physician recommendations regarding adjuvant radiation therapy, according to data presented during the 2025 American Society of Breast Surgeons (ASBrS) Annual Meeting.1 Primary results from the phase II multicenter POWER trial showed that this preoperative window allowed patients to gauge their tolerance to endocrine therapy, leading to increased shared decision-making for postoperative treatment and potentially more personalized and appropriate therapy.
“Patients who tolerate endocrine therapy well during the preoperative period may opt to omit radiation therapy and choose drug therapy with greater assurance in their ability to complete their adjuvant endocrine therapy regimen,” said lead study investigator Shayna L. Showalter, MD, FACS, Professor of Surgery at the University of Virginia. “Conversely, women who experience significant side effects to preoperative endocrine therapy may choose to proceed with radiation therapy to avoid ‘undertreatment’ if they are not able to remain adherent to the adjuvant endocrine therapy. Women do not necessarily need both postoperative therapies, which would represent overtreatment.”
Shayna L. Showalter, MD, FACS
Historically, the standard treatment of estrogen receptor–positive, early-stage breast cancer was breast-conserving surgery followed by adjuvant radiation therapy and 5 to 10 years of endocrine therapy, both known to reduce the risk for recurrence. As Dr. Showalter explained, however, large, randomized trials have shown that radiation therapy may be safely omitted for women aged 65 and older with early-stage, estrogen receptor–positive, invasive breast cancer undergoing lumpectomy if they are committed to adjuvant endocrine therapy.
Study Methods and Results
The POWER trial was designed to assess whether a 90-day period of preoperative endocrine therapy could provide patients and physicians with enough insight into treatment tolerance to inform the decision-making process regarding adjuvant radiation therapy. The trial included women aged 65 and older with estrogen receptor–positive, HER2-negative, invasive breast cancers 2 cm or less who planned to have breast-conserving surgery. The trial accrued 75 women (74 in the final analysis cohort), with a median age of 73.
All participants received 90 days of preoperative endocrine therapy (aromatase inhibitors or tamoxifen) before surgery. Patient and physician preferences for adjuvant radiation therapy were recorded before and after the 90-day endocrine therapy course. Decisions about radiation therapy were made by the patients and their treating physicians. It was recommended—but not required—for patients to undergo adjuvant endocrine therapy after surgery. Patient-reported outcomes on health-related quality of life, decisional conflict, and decision regret were also collected.
As Dr. Showalter reported, 95% of participants completed the 90-day preoperative endocrine therapy course. Adverse events related to endocrine therapy were reported in 47% of patients.
The primary outcome showed a statistically significant change in both patient preference and surgeon recommendation for adjuvant radiation therapy after the 90-day preoperative endocrine therapy period, exceeding the prespecified threshold for significance. A total of 21 patients (28%) changed their preference for radiation. Surgeons changed their recommendation for radiation for 18 patients (24%).
DISCLOSURE: Dr. Showalter reported no conflicts of interest.
REFERENCE
1. Showalter S, et al: 2025 ASBrS Annual Meeting. Abstract 1988340.
EXPERT POINT OF VIEW
Puneet Singh, MD, MS, FACS, FSSO, CMQ, Assistant Professor of Breast Surgical Oncology at The University of Texas MD Anderson Cancer Center in Houston, underscored the clinical significance of the POWER trial results. “The findings of the POWER trial demonstrate that a 3-month preoperative course of endocrine therapy may provide women with low-risk, estrogen receptor–positive breast cancer a window into their ability to tolerate endocrine therapy and empower them in making decisions about adjuvant radiotherapy or endocrine therapy,” Dr. Singh told The ASCO Post.
Puneet Singh, MD, MS, FACS, FSSO, CMQ
According to Dr. Singh, personalizing treatment for older women with low-risk, estrogen receptor–positive breast cancer, which includes de-escalating therapy, is an important goal. However, it can be challenging to know how patients will respond to a particular therapy, especially endocrine therapy.
“The recently published interim analysis of the randomized EUROPA trial by Meattini et al in The Lancet Oncology1 showed that older women treated with single-modality endocrine therapy or radiation therapy after breast-conservation surgery had decreased health-related quality of life with adjuvant endocrine therapy compared with adjuvant radiation therapy,” said Dr. Singh. “Given the known side effects that lead to some patients discontinuing endocrine therapy before 5 years, preoperative endocrine therapy may be an effective strategy to assess tolerance in advance and truly inform them about which adjuvant therapy may be best for them.”
Dr. Singh also noted there were patients who initially preferred radiation therapy but subsequently did not have a favorable preference for it. Therefore, the preferences for adjuvant therapy changed in both directions, Dr. Singh explained.
“Though not all patients may want to delay surgery by 3 months, and it is a small study, the POWER trial provides necessary data on active decision-making in de-escalating therapy for this patient population,” she concluded.
DISCLOSURE: Dr. Singh reported no conflicts of interest.
REFERENCE
1. Meattini I, De Santis MC, Visani L, et al: Single-modality endocrine therapy versus radiotherapy after breast-conserving surgery in women aged 70 years and older with luminal A-like early breast cancer (EUROPA): A preplanned interim analysis of a phase 3, non-inferiority, randomised trial. Lancet Oncol 26:37-50, 2025.
