Clinical Summary:

• Design/Population: Phase 3 noninferiority SENOMAC trial randomizing 2,766 patients with breast cancer and one to two sentinel lymph node macrometastases to completion axillary lymph node dissection or omission of further axillary surgery.
• Key Outcomes: Five-year overall survival was 93.4% with axillary dissection and 94.4% with omission, confirming noninferiority. Patient-reported outcomes consistently favored omission, with clinically meaningful improvements in arm symptoms and function persisting through 5 years.
• Clinical Relevance: These findings support omission of completion axillary lymph node dissection in patients with limited nodal disease, reducing long-term morbidity without compromising oncologic outcomes.

Jana de Boniface, MD, PhD, Capio St Göran's Hospital and Karolinska Institutet, Stockholm, Sweden, discusses final results from the SENOMAC trial evaluating whether completion axillary lymph node dissection can be safely omitted in patients with breast cancer and limited sentinel node involvement. The study enrolled more than 2,700 patients across five countries and was designed to provide definitive evidence regarding the oncologic safety of de-escalating axillary surgery.

Results demonstrated no difference in overall survival, breast cancer–specific survival, or recurrence-free survival between treatment groups, while omission of axillary dissection resulted in significantly better patient-reported outcomes that persisted through 5 years of follow-up. These findings support a less invasive surgical approach for patients with one to two sentinel lymph node macrometastases and reinforce ongoing efforts to reduce treatment-related morbidity in early breast cancer.

Dr de Boniface presented these results at the 2026 ASCO Annual Meeting in Chicago, Illinois.

Transcript:

My name is Jana de Boniface. I'm a surgeon at the Capio St. Göran's Hospital in Stockholm, Sweden, also a clinical professor at the Karolinska Institute. I am here at ASCO 2026 to present the final outcome data of the randomized SENOMAC trial.

The SENOMAC trial is a clinical non-inferiority trial which randomized patients with breast cancer and up to 2 sentinel lymph node macrometastases to either a completion axle lymph node dissection or its omission. Only a sentinel node biopsy. These patients and afterwards received standard of care, for example, radiotherapy or any kind of systemic therapy. We randomized 2,766 patients in 5 countries between 2015 and 2021. Just recently the primary end point results of overall survival have matured. We do see a 5-year overall survival of 93.4 in the completion axle lymph node dissection group and 94.4 in the omission group. There's absolutely no difference between those and non-inferiority was confirmed.

We actually undercut the requirement of the upper limit of the hazard ratio of 1.44 by far because our hazard ratios upper limit of the confidence interval actually ends up on 1.17. That's very reassuring results, especially because this trial is 1 of the only ones that are fully statistically powered. We see exactly the same thing for secondary oncological outcomes such as breast cancer specific survival and recurrence free survival. Now probably even more important are the patient reported outcomes. The trial collected questionnaires, EORTC BR23 and C30 plus a very arm specific questionnaire called Lymph-ICF at 4 different time points. We have an early postoperative assessment 1, 3, and 5 years after the surgery.

We presented yesterday the results all the way to 5 years with very excellent response rates of 81 to 83%. Interestingly, we see very significant differences between the 2 groups at every single time point and these differences are also clinically relevant because they are more than 10 score points at every time. It's interesting to see that the difference between the group is not only something that you see early postoperatively, but it actually persists over time. There's no signal of any reduction of the differences between the group.

We think that omission of axillary lymph node dissection is really relevant for patient reported quality of life. When we look at global health related quality of life, usually the trials do not see a difference, obviously because patients are impacted more by their adjuvant treatment and other life factors than only the axillary surgery. But in this trial, we do actually see statistically significant differences at the early postoperative assessment and also at 3 years. Now I wouldn't say that we should put too much weight on that because even though it's statistical significant, it's a relatively little difference. I wouldn't call it clinically relevant, but it's very interesting to see. We also looked at different subgroups and we don't see any safety signals in any of the subgroups, including, for example, our 919 patients receiving a mastectomy or our 147 patients with T3 tumors.

In conclusion, the trial confirms with very solid statistical power that we should be able to omit completion axial lymph node dissection in all patients with 1 to 2 central lymph node macrometastases.

Source:

de Boniface J, Tvedskov  TS, Rydén L, et al. Omission of completion axillary dissection in patients with breast cancer and sentinel lymph node macrometastases: Overall survival and patient-reported arm morbidity from the randomized SENOMAC trial. Presented at the ASCO Annual Meeting. May 29 - June 2, 2026. Chicago, Illinois. LBA503.