Quick answer
A sentinel lymph node biopsy removes the first one to three lymph nodes that drain the breast, located using a tracer injected before surgery. If those nodes are clear of cancer, the remaining armpit nodes almost always are too, so they can be left alone — which avoids the arm swelling that full clearance can cause.
Key takeaways
- The sentinel node is simply the first node the breast drains into. It is identified, not guessed at.
- A tracer — radioisotope, blue dye, a magnetic tracer, or a combination — is used to find it during surgery.
- One to three nodes are usually removed and examined by a pathologist.
- A clear sentinel node means the rest of the armpit is very likely clear, so no further armpit surgery is needed.
- Lymphoedema risk after sentinel node biopsy is a few per cent, against roughly one in five after full axillary clearance, though published figures vary.
- It is done under general anaesthetic at the same time as the breast operation, usually as a day case.
For decades, surgery for breast cancer meant removing all the lymph nodes from the armpit, because there was no way to know which ones were involved without taking them out. It worked, and it caused a great deal of avoidable harm: permanent arm swelling, shoulder stiffness and numbness in a large number of women whose nodes turned out to be entirely clear.
Sentinel node biopsy solved that problem by asking a smarter question. Instead of removing everything, find the node the cancer would reach first, and let that one node answer for the rest.
What is the sentinel node?
Lymph drains from the breast in an orderly way, and for any given part of the breast there is a first node it reaches. That is the sentinel. It is not a specific anatomical node with a name — it varies from person to person — which is why it has to be located during surgery rather than looked up.
The logic is straightforward. Cancer cells travelling through the lymphatic system arrive at the sentinel node before they can reach any node beyond it. So if the sentinel is clear, the nodes downstream of it are very unlikely to be involved.
How is the sentinel node found?
Step one: the tracer
A tracer is injected into the breast, usually near the nipple or around the tumour. Options include a small dose of radioactive technetium, given a few hours or the day before surgery; a blue dye given at the start of the operation; or a magnetic tracer, which avoids the logistics of handling a radioisotope. Many units use two tracers together because the combination locates the node more reliably than either alone.
Step two: locating it in theatre
Where a radioisotope has been used, a handheld gamma probe is passed over the armpit and identifies the node as a hot spot. Blue dye stains the node visibly, and a magnetic tracer is detected with a magnetometer. Between them, the surgeon can usually identify the node through a small incision in the armpit.
Step three: removing and examining it
The node, and any others that also light up, is removed — typically one to three in total. It goes to the laboratory and is sectioned and examined for cancer cells. Some units perform an assessment during the operation itself so that further armpit surgery can be done in the same anaesthetic; others wait for the full pathology, which is more accurate but may mean a second procedure if the node is involved.
What happens if the sentinel node is clear?
Nothing further is done to the armpit. That is the whole point of the technique: you avoid a full clearance and its consequences. Follow-up continues as normal, and the node result feeds into decisions about chemotherapy, radiotherapy and hormone treatment.
What happens if the sentinel node contains cancer?
It depends on how much, and on the rest of the picture. Options include removing the remaining armpit nodes, treating the armpit with radiotherapy instead of surgery, or in selected cases with very low-volume involvement, no further armpit treatment at all. Radiotherapy to the armpit has been shown to control disease comparably to clearance with less lymphoedema, which is why it is now a standard alternative.
This is a decision taken at a multidisciplinary meeting rather than by one person, and it is exactly the kind of decision where lymph node testing results, imaging and tumour biology all have to be weighed together.
Sentinel node biopsy compared with full clearance
| Sentinel node biopsy | Axillary node clearance | |
|---|---|---|
| Nodes removed | Usually one to three | Typically all nodes in the armpit, often fifteen or more |
| Incision | Small, in the armpit | Larger, in the armpit |
| Drain afterwards | Usually none | Often needed |
| Lymphoedema risk | A few per cent | Roughly one in five, though figures vary |
| Shoulder stiffness | Uncommon and usually temporary | More common and can be persistent |
| Numbness under the arm | Possible, often temporary | More extensive and more often permanent |
| When it is used | Invasive cancer with normal-looking nodes on imaging | Nodes known to be involved, or after a positive sentinel node |
| Recovery | Usually a day case, back to normal in one to two weeks | Longer, with physiotherapy commonly needed |
“The reason this technique matters is not that it finds more cancer. It is that it spares the arm in the majority of women whose nodes were never involved in the first place.”
Mr Debashis Ghosh, Consultant Breast and Oncoplastic Surgeon
If you have been told you need armpit surgery and want the reasoning explained properly, or you want a second view on a treatment plan, a consultation is the place to do it. New breast symptoms are assessed through our same-day one-stop breast clinic. We see our clinic for Westminster patients and patients from across London.
Sentinel node biopsy: frequently asked questions
Is sentinel lymph node biopsy painful?
It is done under general anaesthetic so you feel nothing during it. Afterwards most people describe soreness in the armpit for a week or two, manageable with simple painkillers, and considerably less than after a full clearance.
How many nodes are removed?
Usually one to three. The surgeon removes whichever nodes the tracer identifies, so the number varies. Removing several sentinel nodes is normal and does not mean anything has been found.
Will the blue dye discolour my skin?
If blue dye is used, it can leave a bluish-green tinge in the skin of the breast which fades over weeks to months, and it can turn urine a greenish colour for a day or two. Both are harmless. Units using a magnetic tracer avoid the dye discolouration.
Can I still get lymphoedema after a sentinel node biopsy?
Yes, but the risk is much lower than after a full clearance — a few per cent rather than roughly one in five. Risk rises if you also have radiotherapy to the armpit. Any persistent swelling, heaviness or tightness in the arm should be reported early, because treatment works better when started promptly.
How long do results take?
Several working days for full pathology, because the node has to be processed, sectioned, stained and examined. Some units assess the node during the operation so that further surgery, if needed, can be done in the same anaesthetic.
Do I need a sentinel node biopsy for DCIS?
Usually not. DCIS is non-invasive and by definition has not spread to nodes. It is sometimes performed where a mastectomy is being done for extensive DCIS, because an invasive component is occasionally found in the final specimen and the opportunity to sample the node has then passed.
What if my nodes already look abnormal on the scan?
Then the node is usually biopsied with a needle before surgery. If cancer is confirmed, sentinel node biopsy is not the right test, because the question it answers has already been answered, and the discussion moves to clearance or radiotherapy.
Related reading: Getting a Second Opinion on a Breast Cancer Diagnosis in the UK
Want your treatment plan explained properly?
Consultant-led discussion of your imaging, pathology and the reasoning behind each recommendation.
Sources
- NICE NG101 — Early and locally advanced breast cancer. recommendations on axillary staging and management
- Cancer Research UK — Lymph node removal for breast cancer. what sentinel node biopsy and clearance involve
- NHS — Lymphoedema. symptoms to report and how it is managed
- NHS — Breast cancer treatment. how surgery fits with radiotherapy and drug treatment
This article provides general information and does not replace personalised medical advice, diagnosis or treatment. If you have a breast symptom that concerns you, arrange an assessment.