Dr. Kathleen Horst, Dr. Rachel Jimenez, and Dr. Yara Abdou discuss the updated guideline from ASTRO, ASCO, and SSO on postmastectomy radiation therapy. They share new and updated recommendations on topics including PMRT after upfront surgery, PMRT after neoadjuvant systemic therapy, dose and fractionation schedules, and delivery techniques. They comment on the importance of a multidisciplinary approach and providing personalized care based on individual patient characteristics. Finally, they review ongoing research that may impact these evidence-based guidelines in the future.

Read the full guideline, “Postmastectomy Radiation Therapy: An ASTRO-ASCO-SSO Clinical Practice Guideline” at www.asco.org/breast-cancer-guidelines"

TRANSCRIPT

This guideline, clinical tools, and resources are available at www.asco.org/breast-cancer-guidelines. Read the full text of the guideline and review authors’ disclosures of potential conflicts of interest in the Journal of Clinical Oncology, https://ascopubs.org/doi/10.1200/JCO-25-01747 

Brittany Harvey: Hello and welcome to the ASCO Guidelines podcast, one of ASCO's podcasts delivering timely information to keep you up to date on the latest changes, challenges, and advances in oncology. You can find all the shows, including this one, at asco.org/podcasts.

My name is Brittany Harvey, and today I am interviewing Dr. Kathleen Horst, expert panel chair from Stanford University; Dr. Rachel Jimenez, expert panel vice chair from Massachusetts General Hospital; and Dr. Yara Abdou, ASCO representative from the University of North Carolina, authors on "Postmastectomy Radiation Therapy: An American Society for Radiation Oncology, American Society of Clinical Oncology, and Society of Surgical Oncology Clinical Practice Guideline." Thank you for being here today, Dr. Horst, Dr. Jimenez, and Dr. Abdou.

Dr. Kathleen Horst: Thank you for having us.

Brittany Harvey: And then just before we discuss this guideline, I would like to note that ASCO takes great care in the development of its guidelines and ensuring that the ASCO conflict of interest policy is followed for each guideline. The disclosures of potential conflicts of interest for the guideline panel, including Dr. Horst, Dr. Jimenez, and Dr. Abdou who have joined us here today, are available online with the publication of the guideline in the Journal of Clinical Oncology, which is linked in the show notes.

Then to dive into the content that we are here today to talk about, Dr. Horst, could you start us off by describing what prompted the update for this joint guideline between ASTRO, ASCO, and SSO, and what is the scope of this 2025 guideline on postmastectomy radiation therapy?

Dr. Kathleen Horst: Thank you. This joint guideline was last updated in 2016. Over the past decade, the treatment of breast cancer has evolved substantially. Newer systemic therapy regimens have increasingly personalized treatment based on tumor biology, and local therapy management has explored both the de-escalation of axillary surgery and more abbreviated courses of radiation therapy. Given these advances, it was important to revisit the role of postmastectomy radiotherapy in this modern era of breast cancer therapy.

This updated guideline addresses four key questions, including postmastectomy radiation therapy after upfront surgery as well as after neoadjuvant systemic therapy. It also reviews the evolving role of various dose and fractionation schedules and optimal treatment techniques and dose constraints.

Brittany Harvey: Excellent. I appreciate that background, Dr. Horst. So then, next, Dr. Jimenez, I would like to review the recommendations of this guideline across those four key questions that Dr. Horst just mentioned. So first, what does the panel recommend for PMRT for patients who received initial treatment with mastectomy?

Dr. Rachel Jimenez: The panel provided pretty strong consensus that patients with positive lymph nodes or patients with large tumors involving the skin or the chest wall should receive postmastectomy radiation. However, the panel also recognized that the omission of postmastectomy radiation may be appropriate for select patients who have positive lymph nodes and have an axillary lymph node dissection if they have a low nodal burden and other favorable clinical or pathologic features. For patients without lymph node involvement at the time of surgery and no involvement of the skin or chest wall, postmastectomy radiation was not advised by the panel.

Brittany Harvey: Understood. It is helpful to understand those recommendations for that patient population. Following that, Dr. Abdou, what are the key recommendations for PMRT for patients who received neoadjuvant systemic therapy before mastectomy?

Dr. Yara Abdou: When we think about PMRT after neoadjuvant treatment, the key point is that the initial stage of presentation still matters a lot. So for example, if a patient comes in with more advanced disease, say a large primary tumor, like a clinical T4, or more extensive nodal disease, like an N2 or N3 disease, those patients should get PMRT, no matter how well they respond to neoadjuvant therapy, because we know it reduces the risk of recurrence and that has been shown pretty consistently.

On the other hand, if there are still positive lymph nodes after neoadjuvant treatment, basically residual nodal disease, PMRT is also strongly recommended because the risk of local-regional recurrence is much higher in that setting. The gray area is the group of patients who start with a lower burden of nodal disease, such as N1 disease, but then become node negative at surgery. For those patients, we tend to individualize the decision. So if the patient is young or has triple-negative disease, or if there is a lot of residual disease in the breast even though the nodes are cleared, then radiation is probably helpful. But if everything has melted away with pCR in both the breast and the nodes, then it may be safe to omit PMRT in those patients.

For patients with smaller tumors and no nodal involvement to begin with, like a clinical T1-T2 N0, if they are still node negative after neoadjuvant treatment, then PMRT is generally not recommended because their baseline recurrence risk is low.

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