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Understanding the sentinel lymph node

A single node
to stage the entire axilla

The sentinel lymph node is the first lymphatic relay draining the tumor. If it is free of tumor cells, the probability that deeper nodes are involved is very low. This technique therefore allows precise assessment of the axilla while sparing the vast majority of patients a heavier procedure — axillary dissection.

The principle rests on a simple anatomical reality: if tumor cells travel, they follow a very specific path through the lymphatic network. They pass first through a relay node, located under the arm — this is what we call the "sentinel" node. By identifying and removing it alone, we obtain reliable information about the axilla without removing all the lymph nodes.

The impact on life after surgery is considerable. With axillary dissection (removal of 10 to 20 nodes), the risk of chronic lymphedema — "swollen arm" — is around 20 to 30%. With sentinel node biopsy (1 to 3 nodes removed), that risk drops to 5 to 7%. The scar shrinks from 5–8 cm to 2–4 cm. And recovery is far faster.

A major turning point in recent years: until the 2010s, an involved node automatically meant dissection. That is no longer true. Several landmark trials (ACOSOG Z0011, AMAROS, SENOMAC) have demonstrated that dissection can now be replaced by radiotherapy extended to all nodal regions — with the same disease-control outcomes and far fewer long-term sequelae. This evolution, known as de-escalation, is one of the most important advances in modern breast surgery.

What sentinel node biopsy does not replace. This technique assesses the axilla; it does not treat the tumor itself, which is addressed by a specific breast procedure (lumpectomy or mastectomy) during the same operation. Nor does it replace any adjuvant treatments (radiotherapy, endocrine therapy, chemotherapy), which are decided at the multidisciplinary tumor board based on tumor biology — not just nodal status.

>95 %
Detection rate
The sentinel node is identified in more than 95% of cases. This reliability is what allowed systematic dissection to be abandoned.
5–7 %
Lymphedema risk
Versus 20 to 30% after dissection. A three- to fourfold reduction in the risk of chronic arm swelling.
1–3
Nodes harvested
Versus 10 to 20 in a full dissection. Scar 2 to 4 cm long, under the arm.
Who is it for?

Who benefits from
sentinel lymph node biopsy

Sentinel lymph node biopsy is now offered to the vast majority of women undergoing surgery for an invasive breast cancer, provided the axilla is clinically reassuring — meaning no palpable node on examination and no suspicious node on ultrasound. Recent landmark trials have even taken the logic further: in some highly favorable situations, it is now possible to skip sentinel node biopsy altogether.

Most common setting
The vast majority of invasive breast cancers

When an invasive breast cancer is diagnosed and the axillary assessment (physical exam + ultrasound) shows no suspicious node, sentinel node biopsy is the reference approach. This is the situation encountered in most cases — whether the surgery is a lumpectomy or a mastectomy, and whether the tumor measures a few millimeters or several centimeters.

Frequent indication
Mastectomy for DCIS

For mastectomy performed for extensive ductal carcinoma in situ, sentinel node biopsy is recommended. The reason is straightforward: an invasive focus may be found on the final pathology of the mastectomy specimen, and sentinel node biopsy would no longer be technically feasible retrospectively — since the lymphatic pathways have been altered by surgery.

Can we now skip sentinel node biopsy entirely?

For a long time, the answer was a firm no — sentinel node biopsy was considered mandatory in every invasive breast cancer. That changed in 2023–2024, with the publication of several landmark trials that evaluated complete omission of sentinel node biopsy in carefully selected patients.

The most important of these is the Italian SOUND trial (published in JAMA Oncology in 2023). It compared, in women operated on for a small invasive cancer (up to about 2 cm) with a strictly normal axillary ultrasound, two strategies: standard sentinel node biopsy versus complete omission of any axillary procedure, with simple ultrasound surveillance. The 5-year result: no difference in survival, distant recurrence or disease-free survival.

In practice, omitting sentinel node biopsy can now be discussed for patients who meet several criteria: post-menopausal, ductal invasive cancer (lobular carcinoma remains a specific situation), small tumor with an impeccable axillary ultrasound, and a favorable biological profile (luminal A — hormone-sensitive and slow-growing). In these situations, the patient is spared the axillary scar, the tugging sensations, and even the small risk of lymphedema. Follow-up relies on axillary ultrasound and annual clinical examination.

A parallel American trial, INSEMA (published in the New England Journal of Medicine in 2025), reached similar conclusions for a comparable patient group. These data are progressively being integrated into guidelines, and practice is evolving rapidly.

This is not yet a universal standard. Omitting sentinel node biopsy remains an option discussed case by case, only for highly favorable profiles, and always validated at the multidisciplinary tumor board. For every other situation, sentinel node biopsy remains the reference approach.

What about after chemotherapy given before surgery?

An increasing number of breast cancers are treated with chemotherapy before surgery — referred to as neoadjuvant chemotherapy. The goals are twofold: shrinking the tumor, and — crucially — assessing how sensitive the disease is to the treatment. When a node was suspicious before chemotherapy, the question becomes whether it is still involved afterward.

The answer lies in a technique called TAD — Targeted Axillary Dissection, or "targeted axillary sampling." The principle is this: at the time the suspicious node is biopsied, before chemotherapy, the radiologist deposits a tiny metallic marker (a "clip") in it — a few millimeters in size, harmless, and tolerated permanently by the body. Then, after chemotherapy, in the operating room, both the clipped node (retrieved thanks to radiological mapping) and the standard sentinel node are harvested.

If these nodes are free of disease, chemotherapy has done its job at the axillary level — we stop there, no dissection. If they still contain tumor cells, the next step is discussed — dissection, axillary radiotherapy, or a combination depending on the profile. This approach combines rigor with de-escalation: it spares a dissection to many patients who would have been systematically subjected to it ten years ago.

When sentinel node biopsy is not the right option

In some situations, sentinel node biopsy is not selected and an axillary dissection is performed directly. This concerns mainly cases where nodal involvement has been proven before surgery — by fine-needle aspiration or core biopsy of a suspicious node identified on ultrasound. Without this cytological or histological proof, an upfront dissection is never performed. Dissection is also retained in certain specific forms, such as inflammatory breast cancer.

DCIS (ductal carcinoma in situ) treated by lumpectomy does not warrant sentinel node biopsy — by definition, it is an intraductal disease that cannot migrate to the lymph nodes. Sentinel node biopsy is only discussed when DCIS requires a mastectomy — and only in that setting, for the technical reasons outlined earlier.

Finally, sentinel node biopsy is not performed during a prophylactic mastectomy (in BRCA mutation carriers, for example). The surgical specimen is carefully analyzed, and no axillary procedure is justified as a preventive measure in a patient free of cancer.

The decision is always made at the multidisciplinary tumor board — not by the surgeon alone. The choice between sentinel node biopsy, axillary dissection, omission after chemotherapy (TAD), or complete omission of any axillary procedure (SOUND) is discussed based on your full file: tumor size and type, axillary imaging, biological profile (hormone receptors, HER2, Ki67), age, menopausal status, and the overall treatment plan. The overall trend is clear: do as little as possible whenever scientific evidence allows.

Scientific references

• Gentilini OD, Botteri E, et al. Sentinel Lymph Node Biopsy vs No Axillary Surgery in Patients With Small Breast Cancer and Negative Results on Ultrasonography of Axillary Lymph Nodes (SOUND trial). JAMA Oncology, 2023;9(11):1557–1564.

• Reimer T, Stachs A, et al. Axillary Surgery in Breast Cancer — Primary Results of the INSEMA Trial. New England Journal of Medicine, 2025;392(13):1189–1200.

• Caudle AS, Yang WT, et al. Improved Axillary Evaluation Following Neoadjuvant Therapy Using Selective Evaluation of Clipped Nodes (TAD). J Clin Oncol, 2016;34(10):1072–1078.

• SENORIF 2025–2026 Guidelines — Réseau Francilien des Centres de Sénologie. Management recommendations for breast cancer.

• ASCO Sentinel Lymph Node Biopsy Guideline Update, 2021 — Lyman GH et al. J Clin Oncol, 2021;39(27):3056–3082.

How it works

How it works,
in practice

Sentinel node biopsy involves two steps. First, we "mark" the node so it can be located precisely in the operating room. Then, we harvest it during surgery, at the same time as the breast procedure (lumpectomy or mastectomy). The axillary step itself is quick — 5 to 10 minutes — and is added to the duration of the breast surgery. Admission is most often same-day (outpatient).

Mapping, before surgery

The reference technique uses a radioactive tracer — technetium — injected into the breast the day before or the morning of surgery. The injection is quick, painless, and the radiation dose is very low (well below that of a chest CT scan). The tracer travels naturally through the lymphatic vessels, just as a tumor cell would, and stops in the first node it reaches — the sentinel node. A camera locates it, and a mark may be drawn on the skin.

In the OR, for added precision

Just before the incision, a second product may be injected to make the node visually identifiable. Two options exist today: patent blue dye, used for decades, which stains the node blue but may tint the skin and urine for 24 to 48 hours; or indocyanine green, a more recent fluorescent agent, visible under a special light in the OR, with no lasting discoloration. The combination of radioactive tracer + dye offers a detection rate above 95%.

The harvest

The procedure is performed under general anesthesia, at the same time as the breast surgery. A 2 to 4 cm incision is made under the arm, within a natural skin crease. The surgeon locates the node with a probe that detects the radioactive signal, and visually with the colored dye. Usually 1 to 3 nodes are harvested and sent to pathology. The axillary step itself lasts 5 to 10 minutes — this is the duration of the axillary act alone, added to the breast surgery time.

Analysis and result

The node is analyzed by pathology. The final result is available in 10 to 15 days, and is explained at a dedicated post-operative consultation. The next step depends on what the pathologist finds:

  • Node without tumor cells (most common): no further axillary procedure.
  • Small involvement (isolated cells or micrometastasis): in most cases, still no dissection. The planned radiotherapy is sufficient.
  • More significant involvement (macrometastasis): dissection is no longer automatic. Thanks to recent trials (ACOSOG Z0011, AMAROS, SENOMAC), dissection can now be avoided in favor of radiotherapy extended to all nodal regions (axillary, supraclavicular, internal mammary). This radiotherapy gives the same disease-control outcomes as dissection with far fewer side effects. The decision is made at the multidisciplinary tumor board based on your case.
Anesthesia

General anesthesia, during the same operation as the breast surgery. Mandatory anesthesia consultation no later than 48h before. Report any allergy history.

Duration & stay

Axillary step: 5 to 10 minutes, added to the breast surgery duration. Admission most often outpatient (same-day discharge).

Coverage

100% of the French Social Security base rate within the long-term illness (ALD) framework for breast cancer. Supplementary fees apply (Dr Zeitoun practices in secteur 2) — detailed quote provided at consultation.

When dissection remains necessary

What if an axillary
dissection is necessary?

Axillary dissection — the removal of all nodes under the arm — is sometimes still necessary. It has become far less frequent than fifteen years ago, but it keeps its place in specific, well-defined situations. Here is when, how, and especially how to limit its long-term sequelae.

When is dissection proposed?

Three main situations lead to dissection today:

  • When a node is proven to be involved before surgery — via fine-needle aspiration or core biopsy of a node that looked suspicious on ultrasound.
  • In inflammatory breast cancer.
  • In case of sentinel node mapping failure in the operating room — a rare situation where the sentinel node cannot be identified despite both the radioactive tracer and the colored dye. Dissection is then performed so as not to leave the axilla unexamined.

Outside of these cases, we never convert a sentinel node biopsy into a dissection during surgery if the sentinel node has been properly identified. The definitive analysis takes place in the lab, and any subsequent decision (most often extended radiotherapy) is taken later, at the multidisciplinary tumor board.

How the procedure works

Dissection is performed under general anesthesia, at the same time as the breast surgery. The surgeon removes all the fatty tissue containing the axillary lymph nodes — usually 10 to 20 nodes. The axillary step itself lasts 20 to 30 minutes — this is the duration of the axillary act alone, added to the breast surgery time. The scar is longer (5 to 8 cm), under the arm. A drain is usually left in place for a few days to prevent lymph buildup, extending the hospital stay to one or two nights.

Possible sequelae

Dissection provides complete nodal information, but at a cost. The most common sequelae are:

  • Arm lymphedema ("swollen arm"): 20 to 30% of patients, sometimes permanent.
  • Chronic pain and pulling sensations under the arm.
  • Reduced shoulder mobility.
  • Altered sensation in the arm and under the arm (numbness, tingling), most often partial.
  • Increased vulnerability to infection (even a minor wound can lead to erysipelas).

The compression sleeve: a systematic prevention

After dissection, prescription of a compression sleeve is systematic in my practice. It is a soft, discreet compressive garment that maintains steady pressure on the arm and supports residual lymphatic flow.

The protocol is clear: systematic wear for 2 months post-operatively, the period when the risk of lymphedema developing is highest. Beyond these 2 months, wear is no longer systematic — it is maintained on flights (pressurization promotes lymphatic stagnation) and during unusual physical effort. If lymphedema is nonetheless diagnosed later on, the sleeve becomes curative: worn daily, combined with specialized lymphatic drainage physiotherapy.

The sleeve is not prescribed after sentinel node biopsy alone: the lymphedema risk is too low to justify the constraint.

Seek advice quickly in case of swelling of the arm, hand or fingers, a sensation of heaviness, unusual redness or warmth. Lymphedema caught early responds far better than lymphedema established for years. Specialized physiotherapy with manual lymphatic drainage, combined with compression, gives excellent results — as long as intervention is prompt.

Recovery & precautions

After surgery
— what you need to know

The first weeks

The scar under the arm measures 2 to 4 cm (sentinel node) or 5 to 8 cm (dissection). Post-operative pain is moderate, well controlled by standard painkillers. A simple dressing is kept for a few days; showering is allowed the day after surgery.

It is normal to feel numbness, tingling or a "fallen asleep" sensation on the inner side of the arm in the weeks that follow — this is linked to stretching of a small sensory nerve. Sensation largely recovers within a few months, more completely after sentinel node biopsy than after dissection.

An axillary web syndrome may appear 2 to 6 weeks after surgery: small taut fibrous cords under the arm, visible or palpable, that limit movement. It is benign, common (10 to 20%) and responds well to physiotherapy (gentle stretching, massage).

Return to normal activities is possible at 2 to 3 weeks after sentinel node biopsy, 3 to 4 weeks after dissection. Sports are resumed progressively, depending on wound healing.

Useful precautions

The precautions aim to limit the lymphedema risk, without falling into the opposite extreme. The watchword: use your arm normally, keep it active. Avoiding it is counterproductive. Regular physical activity prevents lymphedema — it does not worsen it.

On the operated side, as much as possible:

  • Avoid blood draws and blood pressure measurements.
  • Avoid injections (vaccines, IV lines) — prefer the other arm.
  • Prevent injuries: gloves for gardening and dishes, prompt disinfection of small wounds.
  • Be careful of insect bites and seek advice in case of redness or local warmth.

After dissection, the compression sleeve is worn systematically for 2 months post-operatively. Beyond that, it is kept for flights and unusual physical effort. If lymphedema is diagnosed later, the sleeve becomes curative: worn daily, alongside specialized physiotherapy.

After sentinel node biopsy alone, the sleeve is not prescribed — the lymphedema risk is too low to justify it.

Seek advice quickly in case of arm swelling, a sensation of heaviness, unusual redness or warmth.

Frequently asked questions

Your questions about the
sentinel lymph node

Principle
What exactly is the sentinel lymph node?
▾

It is the first node in the axilla toward which lymph from the breast is directed. If it is free of tumor cells, the probability that deeper nodes are involved is very low. By removing it alone, we obtain reliable information about the axilla without removing all the nodes — sparing most patients the long-term sequelae of dissection.

First lymphatic relay Reliability > 95% Avoids dissection
Dissection
Does sentinel node biopsy always avoid dissection?
▾

In the vast majority of cases, yes. Even when a sentinel node is found to be involved (micrometastasis or one to two macrometastases), dissection can usually be avoided — in favor of radiotherapy extended to all nodal regions (axillary, supraclavicular, internal mammary). This is the major takeaway of the landmark trials of the past fifteen years (ACOSOG Z0011, AMAROS, SENOMAC). Dissection remains indicated when a node is proven involved before surgery, in inflammatory breast cancer, or in case of sentinel node mapping failure in the operating room.

Extended radiotherapy rather than dissection Ongoing de-escalation Tumor board decision
Lymphedema
What is the risk of lymphedema (swollen arm)?
▾

After sentinel node biopsy alone: 5 to 7%. After dissection: 20 to 30%. A few simple precautions help limit this risk. After dissection, a compression sleeve is systematically prescribed and worn for 2 months post-operatively, then in at-risk situations (flights, unusual physical effort). If lymphedema develops later, the sleeve becomes curative and is worn daily, with lymphatic drainage physiotherapy.

Sentinel: 5–7% Dissection: 20–30% Sleeve systematic for 2 months after dissection
Tracer
Is the radioactive tracer dangerous?
▾

No. The dose used is very low, less than that of a chest CT scan, and eliminated within 24 hours. The injection is quick and painless. No specific precautions are required for your family — including young children or pregnant women.

Very low radiation Eliminated in 24 h No precautions needed
Dye
Why might my urine turn blue-green after the operation?
▾

If patent blue was used in the OR, it is eliminated by the kidneys for 24 to 48 hours — urine may take a blue-green tint, and the breast may stay slightly bluish for a few weeks at the injection site. This is normal and harmless. An alternative, indocyanine green (a fluorescent agent visible under a special OR light), does not cause any lasting discoloration.

Transient discoloration Harmless Alternative: indocyanine green
Chemo
What about after chemotherapy given before surgery?
▾

It depends on the imaging performed after chemotherapy. If no node looks suspicious any longer on ultrasound or MRI, TAD (Targeted Axillary Dissection) can be performed: the standard sentinel node is harvested together with the node that was originally suspicious — located thanks to a small metallic clip placed by the radiologist before chemotherapy. Conversely, if a node is still suspicious after chemotherapy, dissection is performed directly.

TAD if imaging is reassuring Dissection if node still suspicious Clip to locate in the OR
Results
When will I get the final results?
▾

The full result of the node analysis is available 10 to 15 days after surgery. It is combined with the analysis of the tumor itself (size, grade, biological profile) to build the complete treatment strategy. A post-operative consultation is scheduled to walk you through the full report. If a decision has to be made at the multidisciplinary tumor board, it is explained and discussed with you — never imposed.

Result in 10–15 days Dedicated consultation Shared decision-making
Coverage
Is it reimbursed?
▾

Yes. The lymphoscintigraphy, the surgical procedure and the node analysis are covered at 100% of the French Social Security base rate, under the long-term illness (ALD) framework for breast cancer. Dr Zeitoun practices in secteur 2 non-OPTAM — supplementary fees apply. A detailed quote is provided before any procedure. Your private insurance may reimburse all or part of these supplementary fees depending on your contract.

100% of SS base rate (ALD) Quote at consultation Private insurance may cover

Further reading

Reference page
Breast cancer
Understanding the disease, treatments and care pathway — the central page bringing together all the information.
→ Read
Patient article
Lumpectomy or mastectomy?
Both breast surgeries explained simply — indications, procedure and follow-up.
→ Read
Dossier
Breast reconstruction
All reconstruction techniques after mastectomy: implant, DIEP, latissimus dorsi, gracilis.
→ Explore

Let's discuss
your situation

Every breast cancer is unique. The surgical strategy — sentinel node biopsy alone, combined with a lumpectomy or mastectomy, with or without reconstruction — is built during the consultation, based on your file and your priorities.

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