SENOMAC's Mature Survival Data at ASCO 2026 Confirms Many Breast Cancer Patients Can Safely Skip Axillary Dissection
Five-year overall survival was non-inferior when surgeons omitted completion axillary dissection, while severe arm problems fell from 12.6% to 3.6%.
Editor's Note ·
- Correction:
- In "Why It Matters," the article attributes the statement that the findings broaden the evidence base to include patients undergoing mastectomy and those with larger T3 tumors to CancerNetwork's "senomac-reveals-omitting-alnd-yields-non-inferior-survival-in-breast-cancer" article. That specific article does not contain this point. The claim is accurate and is supported by the other cited CancerNetwork article ("omitting-alnd-non-inferiority-fewer-arm-related-complications-breast-cancer"), which reports that prior trials "excluded important subgroups, most notably patients undergoing mastectomy or those with larger primary tumors exceeding 5 cm," as well as by The ASCO Post and OncoDaily. The fact stands; only the cited URL is incorrect.
Overview
Mature survival results from the international SENOMAC trial, presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting as abstract LBA503, found that omitting completion axillary lymph node dissection did not compromise survival in breast cancer patients with limited spread to the sentinel nodes, while sharply reducing long-term arm problems. After a median follow-up of 60.1 months, five-year overall survival was 93.4% in the group that underwent completion axillary lymph node dissection (ALND) and 94.4% in the group whose surgeons omitted it, according to The ASCO Post.
The trial was presented by Jana de Boniface, MD, PhD, of Capio St. Göran’s Hospital and Karolinska Institutet in Sweden, as reported by The ASCO Post.
What We Know
SENOMAC randomized 2,766 patients across five countries between January 2015 and December 2021, according to OncoDaily. The per-protocol population included 2,540 patients, with 1,205 assigned to axillary lymph node dissection and 1,335 assigned to omission, OncoDaily reported. The median age of participants was 61 years, according to CancerNetwork.
Eligible patients had primary breast cancer of any size, no abnormal lymph nodes on palpation, and one to two sentinel lymph node macrometastases greater than 2 mm in diameter, CancerNetwork reported. The primary endpoint was overall survival, with non-inferiority defined by an upper one-sided 90% confidence interval for the hazard ratio below 1.44, according to OncoDaily.
The five-year overall survival rate was 93.4% (95% CI, 91.9%-94.9%) in the completion ALND group versus 94.4% (95% CI, 93.1%-95.7%) in the omission group, with a hazard ratio of 0.89 (95% CI, 0.67-1.17) and a non-inferiority P value below .001, according to CancerNetwork. Five-year breast cancer-specific survival was likewise similar at 97.2% in the ALND group and 97.9% in the omission group, The ASCO Post reported. After the median follow-up of 60.1 months, 196 patients had died, including 75 deaths due to breast cancer, according to OncoDaily.
The survival results came alongside a clear difference in arm morbidity. Severe or very severe problems with arm physical function at five years were observed in 12.6% of patients who underwent ALND versus 3.6% who did not, a difference that was statistically significant, according to CancerNetwork. On the Lymph-ICF arm-function scale, the mean score difference at five years favored the omission group by 10.75 points, The ASCO Post reported.
Most patients in both arms received regional radiotherapy. Adjuvant radiotherapy to the regional nodes was given to 87.9% of patients in the completion ALND arm versus 89.7% in the omission arm, according to CancerNetwork.
de Boniface framed the implication for surgical practice directly. “The key finding is that more axillary surgery in itself does not improve survival in these patients. This is extremely important because it means that axillary surgery should be seen as a diagnostic instrument, not a therapeutic tool,” she said, according to The ASCO Post.
Why It Matters
The findings broaden the evidence base for skipping completion dissection to include groups underrepresented in earlier de-escalation trials, including patients undergoing mastectomy and those with larger T3 tumors, according to CancerNetwork. Jane Lowe Meisel, MD, FASCO, a medical oncologist at Winship Cancer Institute of Emory University, highlighted the quality-of-life stakes, noting that lymphedema can be a lasting and disabling consequence of axillary surgery and that the data support safely avoiding invasive node dissection in eligible patients, as reported by CancerNetwork.
What We Don’t Know
The presentation reported five-year outcomes; longer follow-up will determine whether the survival curves remain non-inferior over a longer horizon. Because nearly all patients in both arms received regional nodal radiotherapy, the results apply to a population in which radiation is part of standard management, and they do not directly address patients managed without it. Subgroup durability across the broadened populations — mastectomy recipients and T3 tumors — will require continued reporting as the trial matures.