Fewer Lymph Nodes, Less Arm Swelling: A New Roadmap for Underarm Breast Surgery

Fewer Lymph Nodes, Less Arm Swelling: A New Roadmap for Underarm Breast Surgery

Assessing the lymph nodes under the arm has long been a standard step in breast cancer, both to understand how far the disease has spread and to plan treatment. But every operation in this area carries a risk of lasting arm swelling (lymphedema), loss of sensation and restricted shoulder movement. Randomized trials over the past twenty years have shown that less surgery is enough for many patients. In October 2026 the Association of Breast Surgery (ABS) in the United Kingdom published an updated guideline that brings this evidence together in a single roadmap. In this article we explain the guideline's main recommendations, which patient needs which operation, the situations in which a sentinel biopsy may not be needed at all, and the changing approach for patients who receive chemotherapy before surgery. You can find the basics of breast cancer in our breast cancer guide (in Turkish).

Why does this topic matter?

The underarm lymph nodes are the first stops for lymph fluid coming from the breast. When breast cancer begins to spread, it usually reaches these nodes first; so what is found here is one of the strongest pieces of information determining the stage of the disease and which treatments will be needed after surgery (breast cancer and underarm lymph nodes, what are lymph nodes?; both in Turkish).

On the other hand, removing all the underarm lymph nodes can permanently disturb the lymph circulation of the arm. As a result, swelling, a feeling of heaviness, restricted movement and recurrent infections can appear; this picture can last for years and clearly affects daily life (what is lymphedema?, why do underarm lymph nodes swell?; both in Turkish). So the most important question of the last twenty years has been: in which patient can the information from the underarm be obtained without sacrificing the health of the arm?

The answer came from successive randomized trials, and every time it pointed to "less surgery is enough." The ABS guideline turns this accumulated evidence into rules that can be applied in daily practice. The guideline covers early-stage (I, IIA, IIB) breast cancer; it also touches on some T3N1 patients, but most of the evidence rests on tumors smaller than 5 cm and on fewer than 3 involved lymph nodes (what has changed in breast cancer treatment in recent years?, in Turkish).

Is underarm surgery necessary for every breast cancer patient?

No. According to current guidelines, if the underarm lymph nodes are normal on examination and ultrasound, a sentinel biopsy, which removes only the 1-3 lymph nodes that act as the first filter, is enough instead of clearing the whole underarm. In selected low-risk patients even this biopsy can be omitted. In some patients in whom involvement is found, radiotherapy is preferred over additional surgery.

Three operations, three different extents

To understand the guideline, three terms need to be told apart. Sentinel lymph node biopsy (SLNB) is the removal of the first-filter lymph nodes marked with a radioactive tracer and/or blue dye; the guideline recommends removing 1-3 lymph nodes, 2 on average. Targeted axillary dissection (TAD) is the removal, in addition to the sentinel nodes, of the lymph node whose involvement was proven at diagnosis and which was marked with a small clip. Axillary lymph node dissection (ALND, underarm clearance) is the removal of all the lymph nodes at levels 1 and 2; the guideline recommends not going up to level 3 routinely unless there is radiological involvement or extensive disease (is sentinel biopsy necessary for every patient?, in Turkish).

What is done before surgery?

The guideline recommends an underarm ultrasound for every newly diagnosed patient and a biopsy of any suspicious-looking lymph nodes. A core needle biopsy is preferred; in experienced hands fine-needle aspiration can give a similar result (what is a biopsy?, in Turkish). It is important that the report states how many lymph nodes look abnormal, because all later decisions change according to this number. If involvement is proven, that lymph node needs to be marked with a clip that can be seen on ultrasound.

Why does the size of the involvement matter so much?

In the pathology report, the size of the tumor focus in the lymph node is divided into three groups: isolated tumor cells of 0.2 mm or less, micrometastasis between 0.2 and 2 mm, and macrometastasis larger than 2 mm. In patients who have surgery first, isolated tumor cells are not counted as "involvement" for staging, and micrometastases also do not require additional treatment. In patients who receive chemotherapy before surgery the rule is reversed: even the smallest focus left there is considered significant, because it shows that the treatment did not produce a complete response.

If surgery comes first: deciding by the sentinel biopsy result

This is the part of the guideline that concerns the largest number of patients. In a patient whose underarm looks normal on examination and ultrasound, a sentinel biopsy is done and the paths divide according to the result.

If there is no involvement, only isolated tumor cells, or involvement below 2 mm, no additional underarm treatment (neither clearance nor radiotherapy) is needed. The guideline states that this applies equally to breast-conserving surgery and mastectomy; this had long been a debated point.

If there is involvement larger than 2 mm in one or two lymph nodes, the decision depends on the features of the patient and the tumor. In patients having breast-conserving surgery, with radiotherapy and drug treatment planned afterwards, who are postmenopausal, with a T1, low-grade (grade 1-2), strongly hormone receptor-positive, HER2-negative tumor and no extension beyond the capsule, no additional underarm treatment is needed. If any one of the features such as being premenopausal, a T2 tumor, high grade, hormone receptor negativity, HER2 positivity, lymphovascular invasion or extension beyond the capsule is present, additional treatment is recommended (reading the pathology report, surgical margin and extension beyond the capsule; both in Turkish).

If three or more lymph nodes are involved or the tumor is larger than 5 cm, underarm clearance is recommended. In patients who have had a mastectomy and have involvement in 1-2 lymph nodes, additional treatment is considered; in this group some patients will receive radiotherapy to the chest wall, so the decision is planned together.

If additional treatment is needed: radiotherapy or surgery?

This is one of the clearest recommendations in the guideline. When additional treatment is needed in patients whose underarm looked normal at diagnosis, radiotherapy to the underarm is preferred over clearance. The reason is the AMAROS trial: in this randomized trial the two methods gave similar disease control, while arm swelling at year 5 was 11.9% in those who had radiotherapy and 24.5% in those who had clearance. At ten years, recurrence in the underarm was low in both groups (radiotherapy 1.82%, clearance 0.93%) and there was no significant difference in overall survival. Radiotherapy has its own burdens too: in the same trial the frequency of second cancers was higher in the radiotherapy arm (12.1% versus 8.3% at 10 years), and shoulder stiffness can occur (how is radiotherapy given?, in Turkish).

When radiotherapy is not suitable or the patient does not accept it, clearance is recommended as the additional surgery. When there is extensive extension beyond the capsule, especially in large tumors, clearance again comes to the fore. When clearance is done, the guideline asks for a clip to be placed on the surgical margin to help radiotherapy planning and for this to be written in the operation note.

So does less surgery lead to recurrence in the underarm?

The common finding of the randomized trials is that recurrence in the underarm stays low with every approach. In the SOUND trial the 5-year recurrence rate was equal (0.4%) in the group with no underarm surgery and the group with a sentinel biopsy. In the INSEMA trial it was 1.0% in the group with no surgery and 0.3% in the sentinel biopsy group. One reason for these low rates is that almost all patients receive radiotherapy and drug treatment; in other words, microscopic disease that may have remained in the underarm is also kept under control by these treatments (drug treatment for involvement of 1-3 lymph nodes, in Turkish).

What happens if involvement was proven at diagnosis?

Here the picture is different. In patients who have a lymph node that looked suspicious on ultrasound and was proven to be involved by biopsy and who will have surgery first, the current standard according to the guideline is still underarm clearance. Whether sentinel biopsy plus targeted dissection can replace clearance in this group has not yet been proven. The ABS particularly recommends that patients with a T1-T2 tumor and 1-2 abnormal lymph nodes on ultrasound take part in the TADPOLE trial, which compares these two approaches. In centers where targeted dissection is already being done, the results are asked to be recorded (what is a clinical trial?, in Turkish).

Can the sentinel biopsy ever be omitted?

This is the new and notable part of the guideline. Two separate situations are described.

Over 70, or with a serious additional illness that limits life: If the underarm is normal on examination and ultrasound, if chemotherapy or a CDK 4/6 inhibitor is not expected, and if the tumor is hormone receptor-positive, HER2-negative, low-grade and T1 (or T2 with breast-conserving surgery and radiotherapy planned), a sentinel biopsy is not needed. In patients who could have surgery only under local anesthesia, a sentinel biopsy is considered both technically difficult and of no benefit, and it is recommended to avoid it. On the other hand, in T2 tumors for which a mastectomy is planned and in T3-T4 tumors the biopsy may still be needed, because the result can change the radiotherapy decision (endocrine treatment without surgery in older age, in Turkish).

Under 70: In patients who are postmenopausal, aged 60 or over, with a T1, low-grade, hormone receptor-positive, HER2-negative tumor and with breast-conserving surgery plus radiotherapy and drug treatment planned, omitting the sentinel biopsy can be considered. This recommendation rests largely on the SOUND and INSEMA trials. The guideline also states that an individual decision can be made for favorable-course, low-grade tumors smaller than 15 mm such as tubular and mucinous, or for a few-millimeter invasive focus found incidentally within a wide in situ area (hormone-positive breast cancer, in Turkish).

What these recommendations have in common is that a sentinel biopsy is meaningful only when its result will change a treatment decision. If the same drug and radiotherapy treatment will be given whatever the result, the biopsy has nothing to add for the patient; on the contrary, it adds the risk of arm swelling and loss of sensation. For this reason the guideline asks for the decision to be made before surgery, in the multidisciplinary board and together with the patient (reading research results correctly, in Turkish).

What changes in patients who receive chemotherapy before surgery?

In some patients chemotherapy is given before surgery; this approach can shrink the tumor and can completely clear the involvement in the underarm (surgery first or chemotherapy first?, in Turkish). The guideline's main recommendation in this section is that the sentinel biopsy be done after chemotherapy, not before; doing it first has not been shown to add anything to treatment decisions.

If the underarm is clear at the start, a sentinel biopsy is done after chemotherapy. If the lymph nodes are clear or contain only fibrous tissue consistent with response to treatment, no additional treatment is needed; if there is fibrosis in two or more lymph nodes, radiotherapy can be considered. If the involvement is below 0.2 mm, radiotherapy can be recommended instead of clearance. With larger involvement, clearance is still the standard.

If involvement was proven at the start and the lymph nodes have returned to normal on imaging after chemotherapy, a targeted dissection can be done in which the marked lymph node is removed together with the sentinel biopsy. To reduce false-negative results, the guideline recommends using a dual tracer and removing at least three lymph nodes if the marked node cannot be found. If no involvement remains in the removed lymph nodes, radiotherapy is the standard approach; if involvement above 0.2 mm remains, clearance is recommended. If the lymph nodes still look abnormal after chemotherapy, a sentinel biopsy is not suitable and clearance is done directly.

Special situations

• In situ disease (DCIS): In limited DCIS treated with breast-conserving surgery, a sentinel biopsy is not routinely needed. If a mastectomy will be done, in intermediate- and high-grade DCIS the biopsy should be done in the same operation, because once the breast is removed it is no longer possible to find the sentinel node. In DCIS forming a palpable mass or wider than 5 cm, and in cases with microinvasion, the decision is individual (in situ and invasive cancer, breast-conserving surgery in DCIS; both in Turkish).
• Breast cancer in pregnancy: In pregnant women with a normal underarm, a sentinel biopsy should be done. A radioactive tracer is considered safe in every stage of pregnancy, whereas blue dye should not be used. In pregnant women with proven involvement, the standard approach is clearance.
• Recurrence in the same breast: In patients who previously had breast-conserving surgery and a sentinel biopsy, a repeat sentinel biopsy is technically possible and dual marking is recommended. In about one third of cases lymph flow can follow an unusual route.
• Inflammatory breast cancer: In this rapidly progressing type the standard approach is clearance after chemotherapy followed by wide radiotherapy; sentinel biopsy has not been evaluated sufficiently in this situation.
• Male breast cancer: A sentinel biopsy is recommended in T1-T2 tumors with a clear underarm. If the involvement is below 2 mm, no additional treatment is needed; with involvement above 2 mm, additional treatment is recommended, and in patients who will receive radiotherapy after mastectomy, radiotherapy is preferred over clearance.

Pathology and radiology: what to look for in the report?

The guideline asks for the sentinel lymph nodes to be sent from the operating room in separate, labeled containers, and for the marked lymph node to be in its own container. In the laboratory each lymph node should be sliced at 2 mm intervals and examined completely; the report should state the number of nodes received and the number of involved nodes. Routine immunohistochemistry is not needed. After chemotherapy, pathology is asked to report whether the clip was found and the fibrotic changes that show the response to treatment (treatment plan according to the pathology result, in Turkish). In lymph node examination during surgery, frozen section is more sensitive than touch imprint cytology; the molecular method OSNA is not considered suitable after chemotherapy.

What should we keep in mind when reading this guideline?

• A national guideline: The recommendations were written according to the health system, device approvals and trial network in the United Kingdom. Practice in Türkiye may differ according to resources and reimbursement conditions.
• Not every recommendation has the same strength: The guideline gives a level of evidence (I-V) and a strength of recommendation (A-E) for each item. Some items rest on large randomized trials, others only on expert opinion.
• There are debated areas: Whether targeted dissection can replace clearance in patients with involvement proven at diagnosis is not yet known; for this reason the guideline directs patients into trials.
• The scope is limited: The recommendations are for early-stage disease. In patients who fall outside the trial criteria, the decision should be made individually in the multidisciplinary board.
• New trials are ongoing: The results of the ATNEC, TADPOLE, POSNOC and ALLIANCE trials may change some recommendations in the coming years (tumor biology or clinical risk?, in Turkish).

The situation in Türkiye

Questions you can ask your doctor

• Has my underarm ultrasound been done; is there a suspicious-looking lymph node and how many?
• Which operation is planned in my case: a sentinel biopsy, a targeted dissection or clearance?
• Will the result of the sentinel biopsy change my treatment plan; and if it will not, is this operation necessary?
• If involvement is found, will radiotherapy or additional surgery be considered as additional treatment?
• What is my risk of arm swelling; will my arm be measured before surgery and how will I be monitored?

Frequently Asked Questions

What is a sentinel lymph node biopsy?

It is the marking and removal of one or a few lymph nodes first reached by the lymph fluid coming from the breast, using a radioactive tracer and/or blue dye. Usually 1-3 lymph nodes are taken. The aim is to learn whether the disease has spread without clearing the whole underarm.

If the sentinel biopsy shows involvement, is the underarm cleared?

Not always. If the involvement is below 2 mm, no additional treatment is needed. If there is larger involvement in one or two lymph nodes, additional treatment may not be needed in low-risk patients; if it is considered necessary, radiotherapy to the underarm is usually preferred instead of clearance.

What is the risk of arm swelling (lymphedema) after underarm surgery?

The most important factor determining the risk is the number of lymph nodes removed. In the AMAROS trial, arm swelling at year 5 was 24.5% in those who had underarm clearance and 11.9% in those who had radiotherapy. With a sentinel biopsy alone the risk is clearly lower.

Can the sentinel biopsy be omitted altogether?

In selected patients, yes. Omitting the biopsy can be considered in patients over 70 who have a serious additional illness and a low-risk tumor; and in patients aged 60 or over who are postmenopausal and have a T1, low-grade, hormone receptor-positive, HER2-negative tumor with breast-conserving surgery and radiotherapy planned.

Glossary

Sentinel lymph node

The lymph node first reached by the lymph fluid coming from the tumor area, acting as the "first filter."

Sentinel lymph node biopsy (SLNB)

Removal and examination of these first lymph nodes, found with tracer substances.

Axillary lymph node dissection (ALND)

The operation in which all the level 1 and 2 lymph nodes in the underarm are removed.

Targeted axillary dissection (TAD)

Removal of the lymph node whose involvement was shown at diagnosis and which was marked, together with the sentinel lymph nodes.

Isolated tumor cells

Very small groups of tumor cells of 0.2 mm or less in a lymph node; not counted as involvement in staging.

Micrometastasis

A tumor focus between 0.2 and 2 mm in a lymph node.

Macrometastasis

A tumor focus larger than 2 mm in a lymph node.

Extension beyond the capsule

The tumor in a lymph node breaking through the outer membrane of the node and reaching the surrounding fat tissue.

Lymphedema

Swelling in the arm resulting from disturbed lymph circulation, which can be lasting.

False negative

Failing to find involvement in the removed lymph nodes although it is actually present.