The SENOMAC Study: Reducing Axillary Surgery in Breast Cancer
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Is It Safe to Omit Axillary Lymph Node Dissection?
Study design
SENOMAC involves patients with breast cancer who have no clinically detected axillary lymph node involvement but have 1 or 2 macrometastatic sentinel lymph nodes on sentinel lymph node biopsy. It is a randomized phase 3 study testing whether completion axillary lymph node dissection is necessary in these patients.
| Item | ALND arm | ALND omission arm | Clinical significance |
|---|---|---|---|
| Number of patients | 1205 patients | 1335 patients | A total of 2540 patients were randomized. |
| Patient profile | T1–T3, clinically node-negative breast cancer; 1–2 sentinel lymph node macrometastases | Patients with limited macrometastatic disease in sentinel nodes. | |
| Extent of surgery | Completion axillary dissection | No additional axillary dissection after sentinel biopsy | The survival contribution of more extensive surgery was tested. |
| Mastectomy | Approximately %36 of patients underwent mastectomy | Provides broader applicability than earlier studies such as Z0011. | |
| Large tumors | The tumor was >5 cm in approximately %6 of patients | Groups less represented in earlier studies, such as T3 patients, were included. | |
| Adjuvant therapy | Contemporary systemic therapy and frequently locoregional radiotherapy in both groups | Results should be interpreted in the context of modern multidisciplinary treatment. | |
It means the presence of a cancer focus larger than 2 mm in a sentinel lymph node. Some earlier de-escalation data were strong in micrometastases or more selected patient groups; the importance of SENOMAC is that it shows axillary dissection can also be omitted in broader patient groups with macrometastases.
Survival results: more extensive surgery did not prolong life
Median follow-up was 60,1 months . Five-year overall survival was reported as %94,4in the axillary dissection omission group and %93,4 in the completion axillary dissection group. HR was 0,89 , and non-inferiority was met. Breast cancer-specific survival was also very similar: %97,9 vs %97,2.
Arm function and quality of life: this is where the real difference lies
The most tangible result of SENOMAC for patients concerns arm morbidity. Patients who omitted axillary dissection had better arm function, fewer arm symptoms, and higher quality of life at 1, 3, and 5 years. At five years, severe or very severe arm function problems were reported as %12,6in the completion ALND group, compared with only %3,6 in the ALND omission group.
Lymphedema is a chronic condition involving swelling and a feeling of heaviness in the arm. It can have lasting effects on pain, numbness, limited movement, infection risk, body image, and daily life. Therefore, an operation that does not improve survival but increases the risk of lymphedema is highly relevant to treatment decisions.
Connection with earlier data: what did SENOMAC expand?
Studies such as ACOSOG Z0011 and AMAROS had shown that axillary dissection could be reduced in selected patients. However, these studies had some limitations: groups such as patients undergoing mastectomy, those with larger tumors, and those with extracapsular extension in sentinel nodes were less represented. SENOMAC expanded the boundaries of axillary de-escalation by including T1–T3 patients, those undergoing mastectomy, and a broader population with sentinel node macrometastases.
| Study / approach | Main contribution | Limitation | Innovation introduced by SENOMAC |
|---|---|---|---|
| Z0011 | Safety of omitting ALND in patients with breast-conserving surgery + limited sentinel node involvement | Limited representation of mastectomy and broader patient groups | SENOMAC also included mastectomy patients. |
| AMAROS | Comparison of axillary radiotherapy with ALND; less lymphedema | Focused on a radiotherapy strategy instead of ALND | SENOMAC directly tested omission of ALND. |
| SENOMAC | Omission of completion ALND with 1–2 sentinel node macrometastases | Should be interpreted in the context of modern adjuvant therapy and radiotherapy | Survival was non-inferior, with substantially lower arm morbidity. |
Critical reading
This result should not be generalized to everyone
- Patient selection matters: SENOMAC includes clinically node-negative patients with 1–2 sentinel node macrometastases. It does not apply directly to patients with clinically evident axillary disease.
- The adjuvant treatment context is critical: Most patients received contemporary systemic therapy and locoregional radiotherapy. This result does not mean “ignoring the axilla completely.”
- Additional nodal information is lost: Additional nodal disease was found in %34,3 of patients who underwent completion ALND. This information may affect some systemic therapy or radiotherapy decisions.
- The radiotherapy question remains open: When ALND is omitted, in which patients can nodal radiotherapy also be reduced? Studies such as T-REX will answer this question.
- There is a separate question in early-stage, low-risk patients: Omitting even sentinel node biopsy in some older, low-risk patients is a different area of de-escalation; SENOMAC should not be confused with this.
Message for clinical practice
SENOMAC shows that completion axillary dissection should no longer be a routine reflex in many breast cancer patients with limited sentinel node macrometastases. In these patients, axillary surgery should be viewed more as a diagnostic/staging procedure than a therapeutic one; decisions about additional surgery should be made together with systemic therapy, the radiotherapy plan, tumor biology, and patient preference.
How should it be explained to the patient?
“Finding a limited number of cancer cells in your sentinel lymph node may not necessarily mean that all the lymph nodes in your armpit need to be removed. In this large study, survival was not worse in patients who did not undergo additional axillary surgery; instead, arm swelling, pain, and movement problems were substantially less frequent. However, the decision must be made together with your tumor characteristics, type of surgery, radiotherapy, and systemic treatment plan.”
Drozdogan Academic Commentary
SENOMAC is a strong de-escalation study showing that the idea that “more surgery leads to better oncological outcomes” is no longer valid for many patients undergoing breast cancer surgery.
The non-inferiority of 5-year overall survival in the ALND omission group and the substantial preservation of arm function suggest that, with limited sentinel node involvement, axillary dissection is often only a staging procedure rather than a therapeutic one.
In the future, axillary management will evolve into a more refined and personalized field shaped by tumor biology, systemic treatment, the radiotherapy plan, and patients’ quality-of-life goals rather than surgical reflexes.
Conclusion
The mature results of SENOMAC presented at ASCO 2026 showed that omitting completion axillary dissection did not worsen survival in clinically node-negative T1–T3 breast cancer patients with 1–2 sentinel lymph node macrometastases. The 5-year OS was %94,4 versus %93,4, and breast cancer-specific survival was %97,9 versus %97,2.
The real difference emerged in quality of life: patients who omitted ALND had better arm function, fewer arm symptoms, and substantially fewer severe/very severe arm function problems at 5 years. These data are a strong ASCO 2026 result that could establish de-escalation of axillary dissection as the new standard in selected patients.
- ASCO Press Release. Some breast cancer patients with sentinel lymph node spread can safely skip axillary lymph node dissection. 30 May 2026.
- Targeted Oncology. Omitting ALND Is Safe and Reduces Arm Complications in Certain Breast Cancer Patients. 30 May 2026.
- ecancer. ASCO 2026: Some breast cancer patients with sentinel lymph node spread can safely skip ALND. 30 May 2026.
- de Boniface J et al. Omitting Axillary Dissection in Breast Cancer with Sentinel-Node Metastases. New England Journal of Medicine. 2024.
- PubMed. SENOMAC primary recurrence-free survival results. 2024.
- drozdogan.com. Early-Stage Breast Cancer: Should Axillary Surgery Be Performed Solely to Decide on a CDK4/6 Inhibitor?
- drozdogan.com. Is It Necessary to Remove All Axillary Lymph Nodes? New Approaches in Breast Cancer.
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