SENOMAC: Sentinel-Node Biopsy Only vs Completion Axillary-Lymph-Node Dissection in Breast Cancer with Sentinel-Node Macrometastases

Primary endpoint (Overall survival): Not yet mature — 5-year OS 92.9% (95% CI, 91.0–94.9) vs 92.0% (95% CI, 89.9–94.1); formal noninferiority testing pending Key secondary (Recurrence-free survival, per-protocol): 89.7% vs 88.7% at 5 years — HR 0.89 (95% CI, 0.66–1.19; P<0.001 for noninferiority) Safety signal: No traditional adverse event data reported; trial is surgical — patient-reported lymphedema and quality-of-life outcomes pending

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Clinical Bottom Line

The SENOMAC trial demonstrates that in patients with clinically node-negative breast cancer and one or two sentinel-node macrometastases, omitting completion axillary-lymph-node dissection does not compromise recurrence-free survival. For breast surgeons and multidisciplinary teams, this means that sentinel-node biopsy alone — when combined with modern adjuvant systemic therapy and regional nodal radiation — provides equivalent disease control without the morbidity of a full axillary dissection.

This trial reshapes the surgical approach to sentinel-node-positive breast cancer by substantially broadening the population eligible for axillary conservation. Unlike its predecessor ACOSOG Z0011, which was limited to patients undergoing breast-conserving surgery with whole-breast radiation, SENOMAC enrolled patients regardless of breast surgery type — including those undergoing mastectomy — and mandated modern nodal radiation protocols. This makes the findings directly applicable to a wider clinical population, including the roughly one-third of sentinel-node-positive patients who undergo mastectomy. The results support current guideline trends toward de-escalation of axillary surgery when appropriate systemic and radiation therapy are delivered.

The key practical concern is ensuring that patients who forgo axillary dissection receive comprehensive regional nodal radiation. Nearly nine in ten patients in both arms received nodal radiation therapy, reflecting the contemporary treatment paradigm that underpins the safety of omitting dissection. Clinicians should also note that roughly one-third of patients undergoing dissection had additional non-sentinel-node metastases — disease that went untreated surgically in the sentinel-node-biopsy-only arm but was effectively managed by adjuvant therapy and radiation. Long-term outcomes including overall survival, lymphedema rates, and quality-of-life data remain pending and will be critical for the definitive assessment of this de-escalation strategy.

Trial Overview

Study Design

• Trial name and registration: SENOMAC, NCT02240472
• Design: Phase 3, randomized, open-label, noninferiority trial; prespecified interim analysis of the secondary endpoint (recurrence-free survival)
• Randomization: 1:1, stratified by country
• Setting: Clinically node-negative (cN0) primary T1 to T3 breast cancer with one or two sentinel-node macrometastases
• Enrollment: 67 sites internationally (Sweden, Denmark, Germany, Greece, Italy)

This publication reports the prespecified analysis of the secondary endpoint of recurrence-free survival. The primary endpoint of overall survival has not yet reached the required number of events for formal noninferiority testing.

Patient Population

Key eligibility: Female and male adult patients with cN0 breast cancer, tumor stage T1, T2, or T3, and one or two sentinel-node macrometastases (metastasis size >2 mm). Preoperative axillary ultrasonography was mandatory. Additional micrometastases and extracapsular extension were permitted. Patients with extraaxillary regional or distant metastases, prior invasive breast cancer, or medical contraindications to radiation therapy or systemic treatment were excluded.

Biomarker selection: Not reported in this publication.

Sample size flow: 6,637 patients were screened → 2,766 randomized (1,382 to sentinel-node biopsy only; 1,384 to completion dissection) → 2,624 in the modified intention-to-treat population → 2,540 in the per-protocol population (1,335 biopsy only; 1,205 dissection).

Baseline Characteristics (Per-Protocol Population)

*Extracapsular extension numbers derived from Figure 3 subgroup denominators; percentages are approximate relative to per-protocol N.

Baseline characteristics were well balanced between the two groups. The majority of patients had ER-positive, HER2-negative disease, T1 or T2 tumors, and a single sentinel-node macrometastasis. Notably, more than one-third of patients underwent mastectomy — a population excluded from several prior axillary surgery trials.

Treatment Protocol

Experimental Arm: Sentinel-Node Biopsy Only (n=1,382 randomized; n=1,335 per-protocol)

Sentinel-node biopsy alone without completion axillary-lymph-node dissection. Adjuvant systemic treatment and radiation therapy were administered according to national guidelines.

• Dose and schedule: Not reported in this publication (surgical intervention).
• Treatment duration: Not reported in this publication.
• Median treatment duration: Not reported in this publication.
• Median relative dose intensity: Not reported in this publication.

Radiation therapy including nodal target volumes was administered to 1,192 of 1,326 patients (89.9%) in this group.

Control Arm: Completion Axillary-Lymph-Node Dissection (n=1,384 randomized; n=1,205 per-protocol)

Sentinel-node biopsy followed by completion axillary-lymph-node dissection. Adjuvant systemic treatment and radiation therapy were administered according to national guidelines.

• Dose and schedule: Not reported in this publication (surgical intervention).
• Treatment duration: Not reported in this publication.
• Median treatment duration: Not reported in this publication.

Radiation therapy including nodal target volumes was administered to 1,058 of 1,197 patients (88.4%) in this group. Additional non-sentinel-node metastases were found on completion axillary-lymph-node dissection in 403 of 1,167 patients (34.5%).

Both arms received approximately equivalent rates of adjuvant systemic therapy (approximately 65% chemotherapy, approximately 93% endocrine therapy, approximately 9% HER2-targeted therapy per the body text of the publication referencing supplementary materials).

A radiation therapy quality control program evaluated 1,154 radiation-therapy plans from 1,360 patients in the per-protocol population. Concordance with the electronic case-report form was 1,146 of 1,154 (99.3%) for breast/chest wall target volumes and 1,115 of 1,154 (96.6%) for nodal target volumes.

Efficacy Outcomes

Primary Endpoint: Overall Survival

Definition: Overall survival (primary endpoint). The primary endpoint was changed from breast cancer–specific survival to overall survival in 2020 on the basis of a recommendation from the independent data and safety monitoring board.

Analysis population: Per-protocol (N=2,540)

Statistical method: Cox proportional-hazards model

Median follow-up: 46.8 months (range, 1.5 to 94.5)

Noninferiority margin: Upper boundary of the hazard ratio 95% CI of 1.44; corresponding to a 2.5 percentage-point difference in 5-year overall survival

Status: Statistical power for this endpoint has not yet been obtained. Formal noninferiority testing is pending. Results presented are descriptive.

Sentinel-node biopsy only: 5-year overall survival 92.9% (95% CI, 91.0 to 94.9) Completion dissection: 5-year overall survival 92.0% (95% CI, 89.9 to 94.1)

Total deaths: 62 in the sentinel-node biopsy–only group and 69 in the dissection group (131 total). Of deaths within 5 years (117 total), 50 were due to breast cancer.

Key Secondary Endpoint: Recurrence-Free Survival (Formally Tested)

Definition: Recurrence-free survival following the updated Standardized Definitions for Efficacy End Points (STEEP) criteria, including invasive recurrence and death.

Analysis population: Per-protocol (N=2,540)

Statistical method: Cox proportional-hazards model, adjusted for country. The proportional-hazards assumption was not violated (P=0.48).

Events required: 190 events of recurrence or death.

Events observed: 191 total. Within 5 years: 180 events (89 [6.7%] in the sentinel-node biopsy–only group; 91 [7.6%] in the dissection group).

Sentinel-node biopsy only: 5-year recurrence-free survival 89.7% (95% CI, 87.5 to 91.9) Completion dissection: 5-year recurrence-free survival 88.7% (95% CI, 86.3 to 91.1)

Comparison: HR 0.89 (95% CI, 0.66 to 1.19; P<0.001 for noninferiority)

The upper boundary of the 95% confidence interval (1.19) was significantly below the prespecified noninferiority margin of 1.44, confirming noninferiority. The point estimate favored the sentinel-node biopsy–only group.

Event Breakdown (Per-Protocol Population)

The regional recurrence rate was notably low in both arms (0.4% and 0.5%), consistent with the high rate of nodal radiation therapy in both groups. Distant recurrence was numerically lower in the biopsy-only group (3.3% vs 4.4%).

Secondary Endpoint: Breast Cancer–Specific Survival

Analysis population: Per-protocol

Sentinel-node biopsy only: 5-year breast cancer–specific survival 97.1% (95% CI, 95.8 to 98.3) Completion dissection: 5-year breast cancer–specific survival 96.6% (95% CI, 95.3 to 97.9)

Formal comparison statistics (HR, p-value) were not reported in this publication.

Sensitivity Analyses

The result in the modified intention-to-treat population (HR 0.89; 95% CI, 0.67 to 1.19) was similar to that in the per-protocol population. A sensitivity analysis adjusting for calendar period yielded an identical HR of 0.89 (95% CI, 0.66 to 1.19). A further sensitivity analysis restricting the dissection group to patients with at least 9 lymph nodes removed produced an HR of 0.82 (95% CI, 0.61 to 1.10), with all confidence intervals remaining below the noninferiority margin.

Safety

This is a surgical trial comparing two extents of axillary surgery. No traditional pharmacological adverse event data (TEAEs, grade ≥3 events, serious AEs, treatment-related deaths, dose reductions, or discontinuations) were reported in this publication.

Patient-reported outcomes on lymphedema and quality of life at 3 years are not yet available. One-year questionnaire data from a Swedish-Danish subpopulation were published separately.

The key safety advantage of sentinel-node biopsy only is the avoidance of the well-established morbidity associated with completion axillary dissection — lymphedema, shoulder dysfunction, numbness, and chronic pain — though quantitative reporting of these outcomes is pending from this trial.

Deaths

Treatment-related deaths were not reported in this publication.

Subgroup Analyses

Prespecified subgroup analyses of recurrence-free survival were performed in the per-protocol population. Hazard ratios compare sentinel-node biopsy only versus completion dissection.

Interaction p-values were not reported in this publication.

The noninferiority finding was consistent across all subgroups examined. Notably, the hazard ratio for patients undergoing mastectomy (HR 0.79; 95% CI, 0.52–1.21) was at least as favorable as that for patients undergoing breast-conserving surgery (HR 0.98; 95% CI, 0.65–1.47), a finding of particular clinical relevance since mastectomy patients were excluded from the landmark ACOSOG Z0011 trial. The results were also consistent regardless of extracapsular extension status, number of macrometastases, or tumor stage.

The ER-positive, HER2-positive subgroup showed a notably lower hazard ratio (0.26; 95% CI, 0.07–0.96) favoring biopsy only, though the small number of events (3 vs 10) limits interpretation.

These subgroup analyses were prespecified and were not powered for formal statistical comparisons. Results should be interpreted as hypothesis-generating.

Key Comparator Trials

Cross-trial comparisons are limited by differences in patient populations, trial designs, and endpoints. These data are presented for context, not for direct statistical comparison.

Contextual Notes

The SENOMAC trial builds upon and substantially extends the evidence established by ACOSOG Z0011, which demonstrated that sentinel-node biopsy alone was noninferior to completion dissection for overall survival in patients with T1–T2 tumors undergoing breast-conserving surgery with tangential whole-breast radiation [4]. Z0011's generalizability was limited by its exclusion of mastectomy patients, allowance of only tangential radiation (which may have inadvertently irradiated a portion of the axilla), and the relatively small number of enrolled patients. SENOMAC addresses each of these limitations: it enrolled patients regardless of breast surgery type, mandated modern nodal radiation therapy for both arms, included T3 tumors, and randomized 2,766 patients — nearly three times the Z0011 enrollment.

The AMAROS trial took a different approach, comparing axillary radiation therapy as a direct replacement for axillary dissection in sentinel-node-positive patients [5]. Both AMAROS and SENOMAC support the concept that axillary dissection can be omitted when regional radiation is delivered, though they differ in the control arm intervention (radiation replacement vs observation with systemic therapy and nodal radiation). The contemporaneous POSNOC trial from the United Kingdom has reported concordant findings, further reinforcing the safety of omitting axillary dissection in this population [6].

Collectively, these trials represent a paradigm shift from surgical to radiation-based and systemic management of the axilla. SENOMAC's contribution is its applicability to the full spectrum of breast surgical approaches and its rigorous noninferiority design with prespecified power for both recurrence-free survival and overall survival.

Grey Zones and Unanswered Questions

1. Overall survival noninferiority is not yet demonstrated. This publication reports the secondary endpoint of recurrence-free survival. The primary endpoint of overall survival requires 190 deaths for formal noninferiority testing; 131 deaths had occurred at the time of analysis (62 + 69). Until OS noninferiority is formally established, the definitive conclusion rests on a secondary endpoint.

2. Patients with three or more sentinel-node macrometastases were excluded. The trial enrolled only patients with one or two sentinel-node macrometastases. Patients with a heavier nodal burden — who carry a higher risk of residual axillary disease — were not studied, and the safety of omitting dissection in this population remains unknown.

3. The role of nodal radiation therapy is confounded by the trial design. Nearly 90% of patients in both arms received nodal radiation, reflecting national guidelines in the participating countries. It is impossible to determine from this trial whether the favorable outcomes in the biopsy-only arm are attributable to radiation therapy compensating for the omitted surgery, to effective systemic therapy, or to the low biological significance of residual axillary disease. Patients who do not receive nodal radiation — a scenario possible in some clinical settings — may not derive the same benefit from omitting dissection.

4. Lymphedema and quality-of-life outcomes are pending. The primary rationale for omitting axillary dissection is to reduce morbidity, particularly lymphedema. The 3-year patient-reported outcome data from SENOMAC have not yet been published. Without quantitative morbidity data, the magnitude of the quality-of-life benefit remains unmeasured within this trial, although it is well established from prior studies that completion dissection substantially increases lymphedema risk.

5. The large asymmetry in per-protocol exclusions raises questions about generalizability of the surgical intervention. Of the 1,384 patients randomized to dissection, 179 were excluded from the per-protocol population (largely due to not undergoing the assigned dissection), compared with only 47 exclusions from the 1,382 randomized to biopsy only. Similarly, 131 patients withdrew consent within 21 days in the dissection arm versus 11 in the biopsy-only arm. This asymmetry reflects the known patient reluctance to undergo axillary dissection and supports the real-world argument for de-escalation, but it also means the per-protocol dissection group may represent a selected population more willing to accept aggressive surgery.

Clinical Implications

Rationale and Clinical Context

Completion axillary-lymph-node dissection has been the standard surgical response to sentinel-node macrometastases since the sentinel-node biopsy technique was validated in the late 1990s. This approach provided staging information and regional disease control but at the cost of significant morbidity — lifelong lymphedema risk, shoulder dysfunction, numbness, and chronic pain. As systemic therapy and radiation techniques improved, the therapeutic contribution of axillary dissection came under scrutiny. ACOSOG Z0011 first challenged the paradigm in 2011, but its narrow eligibility (breast-conserving surgery only, tangential radiation, T1–T2 tumors) left the question open for the large proportion of sentinel-node-positive patients undergoing mastectomy or receiving modern nodal radiation.

SENOMAC was designed to provide a definitive answer across the full spectrum of contemporary breast cancer surgery and adjuvant treatment. By confirming noninferiority for recurrence-free survival in a population that includes mastectomy patients, T3 tumors, and patients receiving protocol-mandated nodal radiation, it provides the evidence base for a broader shift in surgical practice.

Monitoring and Long-Term Follow-Up

With a median follow-up of 46.8 months, the current data capture the early recurrence window but may not fully reflect late events, particularly in the ER-positive population where recurrences continue beyond 5 years. The 5-year breast cancer–specific survival exceeds 96% in both arms, suggesting that late breast cancer deaths are unlikely to alter the noninferiority finding, but continued follow-up remains essential.

Regional recurrence rates were remarkably low (0.4–0.5% in both arms), suggesting that nodal radiation effectively controls residual axillary disease. Clinicians should continue standard surveillance protocols including clinical examination and imaging as indicated, with particular attention to the axilla in the biopsy-only group.

De-Escalation Considerations

This trial provides level 1 evidence for omitting completion axillary dissection in patients with cN0 breast cancer and one or two sentinel-node macrometastases, regardless of whether they undergo breast-conserving surgery or mastectomy. The key conditions that underpin this de-escalation are:

• Comprehensive nodal radiation therapy — approximately 89% of patients in both arms received it
• Guideline-concordant systemic therapy — including chemotherapy, endocrine therapy, and HER2-targeted therapy as indicated
• Preoperative axillary ultrasonography confirming cN0 status
• No more than two sentinel-node macrometastases

Clinicians should not extrapolate these findings to patients with clinically palpable nodes (cN1+), patients with more than two positive sentinel nodes, or patients who will not receive nodal radiation therapy.

Unanswered Questions

The two most practice-relevant open questions are: (1) whether overall survival noninferiority will be formally confirmed when the required event count is reached, and (2) whether the quantitative reduction in lymphedema and improvement in quality of life are as substantial as expected from prior observational data. Both will be answered by planned future analyses of this trial.

Regulatory and Guideline Status

Regulatory

This trial evaluates a surgical strategy (omission of completion axillary dissection) rather than a pharmaceutical product. No drug approval or regulatory submission is applicable.

Guidelines

• NCCN: Current NCCN Clinical Practice Guidelines in Oncology for Breast Cancer (2025/2026) have been evolving toward recommending against routine completion axillary dissection in patients with limited sentinel-node metastases receiving appropriate systemic therapy and radiation. SENOMAC reinforces this trajectory, particularly for mastectomy patients [3]. Specific guideline version and recommendation category should be verified at NCCN.org.
• ESMO/St. Gallen: European guidelines have similarly been moving toward de-escalation of axillary surgery. The SENOMAC data, generated predominantly from Scandinavian centers, are expected to strengthen these recommendations.
• ASCO: Guideline updates incorporating SENOMAC data should be confirmed with the most current ASCO breast cancer guideline publication.

⚠️ Guideline recommendations verified as of March 2026. Confirm current guideline recommendations before clinical application at NCCN.org and relevant professional society websites.

About the Author

Andrew Stevenson is the founder and systems architect of kill-cancer.com, a clinical intelligence platform delivering structured, source-traced oncology trial analysis to practicing clinicians. He holds 17 Google technical certifications in data systems, automation, and applied AI — the engineering foundation behind the extraction and verification pipeline that produces every article on this platform. Every number traces directly to its source publication. Zero calculation. Zero editorializing. Zero hallucination.

Five siblings lost to cancer built the urgency. The engineering builds the trust.

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Disclaimer

This article is intended for healthcare professionals only. It is not medical advice and should not be used as a substitute for professional clinical judgment. Treatment decisions should be made in consultation with qualified healthcare providers based on individual patient circumstances.

All trial data presented in this article are sourced directly from the published clinical trial report and its supplementary materials. Numbers are reproduced exactly as reported; no calculations, derivations, or estimates have been performed.

Trial results are presented as reported in the source publication. Updated data, label changes, or guideline revisions published after the source article may alter clinical applicability.

Comparator trial data presented in Section 8 are sourced from their respective published reports and are provided for contextual purposes only. Cross-trial comparisons have inherent limitations and should not be interpreted as direct statistical comparisons.

References

1. de Boniface J, Filtenborg Tvedskov T, Engberg Damsgaard T, et al. Omitting Axillary Dissection in Breast Cancer with Sentinel-Node Metastases. N Engl J Med. 2024. doi:10.1056/NEJMoa2313487
2. Not applicable — this trial evaluates a surgical strategy, not a pharmaceutical product.
3. NCCN Clinical Practice Guidelines in Oncology: Breast Cancer. National Comprehensive Cancer Network. Accessed March 2026.
4. Giuliano AE, Ballman KV, McCall L, et al. Effect of Axillary Dissection vs No Axillary Dissection on 10-Year Overall Survival Among Women With Invasive Breast Cancer and Sentinel Node Metastasis: The ACOSOG Z0011 (Alliance) Randomized Clinical Trial. JAMA. 2017;318(10):918-926.
5. Donker M, van Tienhoven G, Straver ME, et al. Radiotherapy or surgery of the axilla after a positive sentinel node in breast cancer (EORTC 10981-22023 AMAROS): a randomised, multicentre, open-label, phase 3 non-inferiority trial. Lancet Oncol. 2014;15(12):1303-1310.
6. Goyal A, Dodwell D, Reed MW, Coleman RE. Axillary treatment for patients with early breast cancer and one or two positive sentinel nodes (POSNOC): a pragmatic, multicentre, non-inferiority, randomised controlled trial. Lancet. 2023;402(10400):546-554.