Even women with smaller breast cancer tumors and three or fewer lymph nodes involved can benefit from radiation therapy after mastectomy, according to the results of new guidelines published by the American Society of Clinical Oncology, the American Society for Radiation Oncology, and the Society of Surgical Oncology in their respective journals.

The expert panel found sufficient evidence to show that postmastectomy radiotherapy (PMRT) decreases the risk of locoregional failure (LRF), breast cancer recurrence, and mortality, even for patients who previously wouldn’t have received radiation treatment under older recommendations (T1–2 breast cancer with one to three positive axillary nodes).

The expert panel emphasized that the decision to have radiation therapy still needs to be made as part of the larger cancer care team, including practitioners from surgery, radiation, and oncology. They also stressed that the risks and benefits need to be weighed for each patient, citing side effects that include redness, swelling, and skin breakdown severe enough to compromise future breast reconstruction.

“Some subsets of these patients are likely to have such a low risk of LRF that the absolute benefit of PMRT is outweighed by its potential toxicities,” the experts wrote in the guidelines. “Clinicians should consider factors that may decrease the risk of LRF, attenuate the benefit of reduced breast cancer–specific mortality, and/or increase risk of complications resulting from PMRT.”

The new guidelines also offer recommendations for patients who do not receive axillary dissection after a positive sentinel node biopsy: such patients should receive PMRT “only if there is already sufficient information to justify its use without needing to know additional axillary nodes are involved. Patients with axillary nodal involvement after neoadjuvant systemic therapy should receive PMRT.”

Although the guidelines don’t offer a single formula to determine which patients need radiation therapy, they do provide clarity on what was previously a gray area—women who had fewer lymph nodes involved and whether they were at sufficient risk to warrant radiation.