Three leading national cancer organizations today issued an updated guideline on post-mastectomy radiation therapy (PMRT) for physicians treating patients with breast cancer. The recommendations outline when PMRT is appropriate based on new evidence and evolving clinical practice, and they highlight best practices for delivering radiation after breast removal surgery in a multidisciplinary, patient-centered setting.

The American Society for Radiation Oncology (ASTRO), the American Society of Clinical Oncology (ASCO) and the Society of Surgical Oncology (SSO) jointly published the guideline in their respective journals: Practical Radiation Oncology (article link), the Journal of Clinical Oncology (article link) and Annals of Surgical Oncology (article link).

Each year, more than 100,000 people in the United States undergo mastectomy for breast cancer. PMRT is a standard component of care for many patients at higher risk of recurrence, particularly those with cancer in the lymph nodes. By directing radiation to areas where cancer is most likely to return, PMRT can help eliminate microscopic cancer cells that may remain after surgery, reducing a patient’s risk of local recurrence and supporting long-term survival.

“Radiation therapy after a mastectomy can substantially reduce the risk of cancer returning and extend survival for many patients with invasive breast cancer,” said Rachel B. Jimenez, MD, co-chair of the expert panel that developed the guideline update and a radiation oncologist at Massachusetts General Hospital. “At the same time, the benefit of PMRT depends on a patient’s disease characteristics and personal preferences, which is why evidence-based, individualized decisions are so important.”

The updated guideline reflects advances in diagnostics that help physicians identify which patients are most likely to benefit from PMRT after upfront surgery. It also reviews treatment approaches that reduce side effects and improve outcomes, such as advances in radiation techniques, less invasive axillary surgery and more tailored systemic therapies.

“These recommendations help bring clarity to a complex decision, distilling the latest evidence to provide multidisciplinary treatment teams with a roadmap to guide when and how PMRT should be used. The result is treatment that’s better tailored to risk, safer for patients and more effective in the long term,” said Kathleen C. Horst, MD, co-chair of the expert panel and a radiation oncologist at Stanford University.

“PMRT remains a critical component of treatment for most patients with node-positive breast cancer and select patients with high-risk disease, according to new guidelines,” said Sarah E. Schellhorn, MD, a medical oncologist at the Yale School of Medicine and the ASCO representative on the guideline’s expert panel. “The goal of these recommendations is to provide radiation oncologists with clear guidance on appropriate target volumes, dosing, and treatment techniques, in both patients who have not received any systemic treatment and in those who have received neoadjuvant chemotherapy.”

“This guideline includes the most recent and relevant data to continue to advance our ability to individualize care for breast cancer patients while still recognizing the gaps in our current knowledge,” said Cindy Matsen, MD, SSO’s representative on the guideline’s expert panel.

Key recommendations from the guideline update are as follows:

• Patients with node-positive disease (pN+): PMRT is recommended to reduce the risk of recurrence and breast cancer death. Omission may be appropriate for select patients with low recurrence risk, depending on patient and tumor characteristics.

• Patients with node-negative disease: PMRT is recommended for those at higher risk of local recurrence, such as patients with larger tumors (pT3-4) or younger age. In these cases, treatment may target a smaller area (e.g., chest wall alone). PMRT is generally not advised for pT1-2 tumors without nodal involvement, except when multiple high-risk features are present.

• Patients receiving neoadjuvant systemic therapy: PMRT is recommended for patients with locally advanced disease at diagnosis or with residual nodal disease after systemic therapy.

• Dosing and fractionation: The recommendations outline suggested treatment volumes and fractionation approaches. Moderate hypofractionation is generally preferred, with conventional fractionation acceptable in rare cases. The guideline also discusses when a radiation boost to the chest wall or axillary nodes may be warranted, such as when extensive residual disease is suspected or confirmed.

• Optimal techniques: The expert panel also provides guidance on best practices for treatment delivery, recommending CT-based volumetric planning for all patients as well as intensity-modulated radiation therapy (IMRT), daily image guidance and deep inspiration breath hold for select patients to maximize precision and minimize side effects.

• Shared decision making: PMRT decisions should involve providers from all treating disciplines as well as the patient, with discussion of risks and benefits to determine the best treatment approach.

The guideline was developed by a multidisciplinary panel of academic and community-based radiation, medical and surgical oncologists, a medical physicist and a patient representative, based on a systematic review of research published between 2005 and 2024. The guideline is endorsed by the American Society of Breast Surgeons and the Royal Australian and New Zealand College of Radiologists. The original guideline was published in 2001 and updated in 2016.

ABOUT ASTRO
The American Society for Radiation Oncology (ASTRO) is the world’s largest professional society dedicated to advancing radiation oncology, with 10,000 members including physicians, nurses, physicists, radiation therapists, dosimetrists and other professionals who work to improve patient outcomes through clinical care, research, education and policy advocacy. Radiation therapy is integral to 40% of cancer cures worldwide, and more than one million Americans receive radiation treatments for their cancer each year. For information on radiation therapy, visit RTAnswers.org. To learn more about ASTRO, visit our website and media center and connect with us on social media.

ABOUT ASCO
Founded in 1964, the American Society of Clinical Oncology, Inc. (ASCO®) is committed to the principle that knowledge conquers cancer. Together with the Association for Clinical Oncology, ASCO represents more than 50,000 oncology professionals who care for people living with cancer. Through research, education, and promotion of high quality patient care, ASCO works to conquer cancer and create a world where cancer is prevented or cured, and every survivor is healthy. Conquer Cancer, the ASCO Foundation, supports ASCO by funding groundbreaking research and education across cancer’s full continuum. Learn more at www.ASCO.org, and follow us on Facebook, X, LinkedIn, Instagram, Bluesky, and YouTube.

ABOUT SSO
The Society of Surgical Oncology (SSO) is a dynamic global community of cancer surgeons shaping advancements in the profession to deliver the highest quality surgical care for cancer patients. SSO promotes leading-edge research, quality standards and knowledge exchange, connecting cancer surgeons worldwide to continuously improve cancer outcomes. Learn more at www.surgonc.org.