Rachel B. Jimenez, MD
Kathleen C. Horst, MD
A joint task force composed of experts from the American Society of Radiation Oncology (ASTRO), ASCO, and the Society of Surgical Oncology (SSO) has released new guidance for postmastectomy radiation therapy (PMRT) for patients with breast cancer.1 This guideline—which is intended to replace the joint PMRT guideline developed in 2016—reflects the latest evidence on therapy de-escalation, personalized treatment decision-making, and more.2
“We hope that oncologists will find the guideline to be a clear and helpful reference, providing evidence-driven recommendations for the utilization of postmastectomy radiation in the modern era,” said Task Force Vice Chair Rachel B. Jimenez, MD, of Massachusetts General Hospital.
Ushering in a New Era
The diagnosis, treatment, and long-term management of breast cancer have undergone substantial transformation over the past few decades, resulting in more precise detection methods and highly personalized therapeutic options.3 This transformation includes clinical trials supporting the use of and innovations in PMRT for disease control and improved survival.4
According to Guideline Task Force Chair Kathleen C. Horst, MD, of Stanford Medicine, a plethora of practice-changing clinical trial data published over the past decade served as a major impetus not just to update but instead to completely replace the 2016 guideline.
“Changes from these clinical trials have included new systemic therapies, recognition of the importance of breast cancer biologic subtypes driving outcomes, and de-escalation of axillary surgery,” she said. “Given these advances, it was important to reassess the role of PMRT in the modern era.”
Furthermore, Dr. Horst explained, the data previously used to inform clinical decision-making for PMRT were from a time when older systemic therapy regimens were relied upon.
Like its predecessor, the latest guideline was developed collaboratively, with representatives from ASTRO, SSO, and ASCO combing through the published evidence, synthesizing empirical findings with their clinical expertise, and iteratively reviewing and refining the recommendations.
One new key recommendation is that some patients who undergo surgery upfront and who have node-positive disease may be able to safely omit PMRT, as can certain individuals with node-positive disease that converts to node-negative disease following neoadjuvant chemotherapy.
Additionally, in what Dr. Horst described as a “major change from the 2016 guidelines,” the task force found that data now support the use of an abbreviated course of PMRT (3 weeks vs the standard 5 weeks) for most patients. “It is our sincere hope that practitioners embrace this recommendation in order to decrease the time, travel, and financial burden on appropriate patients,” Dr. Jimenez added.
Enhancing Patient Care
The new guideline will likely influence clinical practice in several important ways. First, highlighting when omission of PMRT is safe and appropriate means many patients will be spared unnecessary treatment. Second, the guideline’s recommendations should help clinicians better individualize radiotherapy based on tumor biology rather than reliance on the traditional TNM staging system. Finally, the guideline provides a first-time discussion of optimal radiation planning techniques for PMRT delivery, including target coverage and dose constraints, to encourage the use of modern radiotherapy approaches for breast radiotherapy.
Although Dr. Horst and Dr. Jimenez expressed excitement about the potential ways the guideline could positively shape patient care going forward, they noted that, given the methodology, the task force was limited to reviewing published data during a predefined search window that included publications before October 15, 2024. This means they were not able to “fully capitalize on certain key trials” that were unpublished at that time, Dr. Horst said. These key trials could produce evidence that is critical for radiation treatment decisions, and their corresponding publications must be considered in future guideline updates.
For example, the SUPREMO trial randomly assigned patients with intermediate-risk breast cancer to PMRT vs no radiotherapy.5 This trial was presented at the 2024 San Antonio Breast Cancer Symposium and will provide more guidance on PMRT for this intermediate-risk group.
The RT CHARM trial, which randomly assigned patients who underwent mastectomy and reconstruction to 5 weeks of radiotherapy vs a 3-week course of treatment, was presented at the 2024 ASTRO Annual Meeting.6 It will provide more data on the role of hypofractionated radiotherapy after mastectomy and reconstruction.
Finally, the TAILOR RT trial (ClinicalTrials.gov identifier NCT03488693), which is currently recruiting, will compare the effects of PMRT vs no radiotherapy among patients with node-positive disease and a low-risk, 21-gene recurrence score.
“Additional areas of research that will be important moving forward include the role of PMRT with limited axillary surgery and the interaction of radiotherapy and newer systemic therapy agents,” Dr. Horst added.
Despite these lingering knowledge gaps, the guideline is anticipated to help ensure patients receive care that not only aligns with the latest advances in breast cancer research but also reflects the expertise of clinicians and researchers across multiple disciplines. “We want to thank ASCO for partnering with us on this guideline, as the management of breast cancer continues to be an evolving discussion within multidisciplinary care teams, particularly given the advances in locoregional care as well as systemic therapies in the modern era,” Dr. Horst said.
REFERENCES
1. Jimenez RB, Abdou Y, Anderson P, et al: Postmastectomy radiation therapy: An ASTRO-ASCO-SSO clinical practice guideline. J Clin Oncol. September 16, 2025 (early release online).
2. Recht A, Comen EA, Fine RE, et al: Postmastectomy radiotherapy: An American Society of Clinical Oncology, American Society for Radiation Oncology, and Society of Surgical Oncology focused guideline update. J Clin Oncol 34:4431-4442, 2016.
3. Chopra S, Khosla M, Vidya R: Innovations and challenges in breast cancer care: A review. Medicina (Kaunas) 59:957, 2023.
4. Remick J, Amin NP: Postmastectomy breast cancer radiation therapy. StatPearls, January 2, 2023. Available at https://www.ncbi.nlm.nih.gov/books/NBK519034/. Accessed September 17, 2025.
5. Kunkler I, Russell N, Anderson N, et al: Does postmastectomy radiotherapy in ‘intermediate-risk’ breast cancer impact overall survival? 10 year results of the BIG 2-04 MRC SUPREMO randomised trial: on behalf of the SUPREMO trial investigators. Clin Cancer Res 31(suppl 12):GS2-03, 2025.
6. Poppe MM, Le-Rademacher J, Haffty BG Jr, et al: A randomized trial of hypofractionated post-mastectomy radiation therapy in women with breast reconstruction (RT CHARM, Alliance A221505). Int J Radiat Oncol Biol Phys 120:S11, 2024.
Originally published in ASCO Daily News. © American Society of Clinical Oncology. ASCO Daily News, September 16, 2025. All rights reserved.
