The 2001 American Society of Clinical Oncology clinical practice guideline on postmastectomy radiotherapy has been updated to help clinicians and patients decide which cases of T1-T2 breast cancer with one-three positive axillary lymph nodes will not benefit from the treatment. Recent evidence suggests that some subsets of this patient group are likely to have such a low risk of locoregional recurrence that the potential adverse effects of radiotherapy would outweigh its benefit.

“We still don’t have a single, validated formula that can determine who needs postmastectomy radiotherapy, but we hope that the research evidence summarized in this guideline update will help doctors and patients make more informed decisions,” Abram Recht, MD, cochair of the expert panel that developed the update, said in a press statement.

“Thanks to advances in systemic therapy, fewer women need radiation therapy after a mastectomy. This means we can be more selective when recommending this treatment to our patients,” said Dr. Recht of Beth Israel Deaconess Medical Center, Boston.

ASCO, in collaboration with the American Society for Radiation Oncology and the Society of Surgical Oncology, reviewed the literature since 2001, including a meta-analysis of 22 clinical trials involving 8,135 patients who were randomly assigned to receive or not receive postmastectomy radiotherapy. “Our panel focused on the results for the 3,786 women who underwent axillary dissection.” The 10-year rate of locoregional treatment failure was only 4.3% with irradiation, compared with 21.0% without irradiation. The 10-year rate of local or distant treatment failure was 33.8% with irradiation and 45.5% without it, and the 20-year rates of breast cancer mortality were 41.5% and 49.4%, respectively.

“The panel unanimously agreed that the available evidence shows that postmastectomy radiotherapy reduces the risks of locoregional failure, any recurrence, and breast cancer mortality for patients with T1-T2 breast cancer and one-three positive lymph nodes,” according to the guideline.

However, clinicians and patients “should consider factors that may decrease the risk of locoregional failure, attenuate the benefit of reduced breast cancer–specific mortality, and/or increase the risk of complications.” These include older patient age, limited life expectancy, coexisting conditions that affect the risk of complications, small tumor size, absence of lymphovascular invasion, small nodal metastases, substantial response to neoadjuvant systemic therapy, low tumor grade, or strong tumor sensitivity to hormonal therapy, Dr. Recht and his associates said (J Clin Oncol. 2016 Sep 19. doi: 10.1200/JCO.2016.69.1188 ).

The guideline also addressed other areas of controversy.

Some clinicians now omit performing axillary lymph node dissection if one-two sentinel nodes are positive, “primarily based on extrapolation of data from randomized trials of patients treated exclusively or predominantly with breast-conserving surgery.” In such cases, the updated guideline “recommends that these patients receive postmastectomy radiotherapy only if there is already sufficient information to justify its use without needing to know that additional axillary nodes are involved.”

Many clinicians are uncertain whether to pursue postmastectomy radiotherapy in patients who have received neoadjuvant systemic therapy, because observational studies suggest the risk of locoregional recurrence is low for those who either have clinically negative nodes before undergoing the treatment or have a complete pathologic response to it in the lymph nodes. The panel decided that current evidence is insufficient to recommend whether radiotherapy should be administered or can be omitted in these groups.

The guideline also recommends that regional nodal irradiation generally should target both the internal mammary and the supraclavicular-axillary apical nodes, in addition to the chest wall or reconstructed breast. “There may be subgroups that will experience limited, if any, benefits from treating both these nodal areas, compared with treating only one or perhaps treating only the chest wall or reconstructed breast. [However,] there is insufficient evidence at this time to define such subgroups in detail.”

Copies of the updated guideline, as well as additional information such as details regarding the panel’s methodology, evidence tables, and clinical tools, are avail at and .

This work was supported by the American Society of Clinical Oncology, the American Society for Radiation Oncology, and the Society of Surgical Oncology. Dr. Recht reported serving as a consultant or advisor to CareCore and U.S. Oncology and receiving research funding from Genomic Health; his associates reported ties to numerous industry sources.