Breast Care A-Z · Procedure · SLNB

Sentinel lymph node biopsy

also: SLNB, sentinel node biopsy, sentinel node sampling · pronounced SLNB (spelled out: S-L-N-B) or 'sentinel node biopsy'

Sentinel lymph node biopsy is a standard part of surgery for most patients with early invasive breast cancer. Its purpose is to give the most accurate picture of whether cancer has spread, while sparing patients the higher side-effect burden of removing all the lymph nodes in the armpit (a full axillary clearance).

Quick answers

Is sentinel lymph node biopsy done at the same time as breast surgery?

Yes, almost always. In most cases the sentinel lymph node biopsy is performed immediately before or after the breast operation itself, under the same general anaesthetic. Occasionally, it is done as a separate operation — for example, if the cancer diagnosis was made from a different procedure.

What happens if cancer is found in the sentinel node?

The next step depends on how many nodes are involved and how much cancer is present. Options include further surgery to remove more nodes (axillary clearance), radiotherapy to the armpit, or, sometimes, no further armpit surgery — the decision is made at a multidisciplinary team meeting with input from oncology.

What is the risk of lymphoedema after sentinel lymph node biopsy?

The risk is substantially lower than after full axillary clearance, but it is not zero. Most patients do not develop lymphoedema; a smaller group does, and it is usually milder than after a full clearance. Any arm swelling, heaviness, or tightness should be reported so it can be assessed early.

SURGERY · AXILLARY STAGING PLATE LI sentinel lymph node biopsy SLNB · sentinel node biopsy targeted sampling of the first-draining axillary lymph node to accurately stage the axilla while minimising surgical morbidity Encyclopaedia of the Breast · Breastory · clinically authored FIG 01 Breast and Axilla — Dual-Tracer SLNB Diagram tumour sentinel node axillary chain (not sampled) Patent Blue V dye injection gamma probe (Tc-99m) hot + blue Callouts i primary tumour (shown in breast parenchyma) ii afferent lymphatic channel (dashed, traced to axilla) iii sentinel lymph node — hot (isotope) and blue (dye), 1–3 nodes excised iv gamma probe detecting Tc-99m radioactivity intraoperatively v axillary lymph node chain — downstream nodes, not sampled in SLNB Dual tracer: Patent Blue V (visible blue colour) + Tc-99m radioisotope (gamma probe signal). Combined detection rate >95%. Sentinel node = first node to receive lymphatic drainage from the tumour. 1–3 nodes typically excised. Blue dye injected peritumorally; isotope injected day before or day of surgery (nuclear medicine dept). SLNB performed under general anaesthesia; small axillary incision. Intraoperative histology determines next step. If sentinel node clear: no further axillary surgery. If macrometastasis (>2 mm): ALND or axillary RT considered. SPIO (Sentimag) and ICG fluorescence now available as non-radioactive alternatives at specialist centres. False-negative rate ~5–10%; influenced by technique, node count and tumour biology. ACOSOG Z0011: patients with 1–2 positive sentinel nodes undergoing BCS + RT may avoid ALND. Dual-Tracer Technique Patent Blue V dye — turns node visibly blue Tc-99m radioisotope — detected by gamma probe Both tracers increase detection rate to >95% SPIO/Sentimag — non-radioactive alternative ICG fluorescence — emerging technique Dual tracer preferred (NICE NG101) Intraoperative Assessment Frozen section / imprint cytology If clear: no ALND — procedure complete Micrometastasis (0.2–2 mm): discuss MDT Macrometastasis (>2 mm): ALND or RT Z0011: 1–2 pos in BCS+RT → no ALND Failed mapping → axillary sampling FIG 02 SLNB vs Axillary Lymph Node Dissection (ALND) Characteristic SLNB ALND Nodes removed 1–3 (sentinel only) Levels I–III (10–20+) Lymphoedema risk <5% 15–25% Numbness Minimal Common Operating time Shorter Longer Hospital stay Day case 1–2 days Accuracy >95% detection rate Full clearance of axilla Seroma Less common More common Shoulder mobility Preserved May be restricted Morbidity Low Higher Use cN0 (node-negative) cN+ or SLNB positive False-negative rate ~5–10% N/A (full dissection) FIG 03 Node Status and Management Finding Histology Action Negative No metastasis No ALND Isolated tumour cells <0.2 mm No ALND Micrometastasis 0.2–2 mm Discuss at MDT Macrometastasis >2 mm ALND or axillary RT Post-neoadjuvant May convert N+ to N0 Re-SLNB ± clip localisation Dual sentinel nodes Both negative No ALND Z0011 criteria met 1–2 positive, BCS + RT No ALND (ACOSOG Z0011) One pos, one neg Micrometastasis MDT decision Failed mapping No sentinel found Axillary sampling FIG 04 SLNB Pathway — 6 Steps Step 1 cN0 confirmed (USS ± FNA) Step 2 Dual-tracer injection (day of / day before) Step 3 Intraop: gamma probe + blue dye ID Step 4 Sentinel node excision (1–3) Step 5 Histology: frozen section or paraffin Step 6 ALND if macro-met / discharge if neg cN0 = clinically node-negative on preoperative imaging. FNA = fine needle aspiration. Frozen section results available intraoperatively. If paraffin (no frozen section), ALND decision deferred to second operation if macrometastasis found. FIG 05 Technique Variants Standard SLNB Dual tracer (blue + Tc-99m) Detection >95% Radioisotope alone Tc-99m only Used where dye unavail. SPIO / Sentimag Non-radioactive Magnetic detection ICG Fluorescence Near-infrared imaging Emerging technique Frozen section Intraop histology Same-op ALND if pos Post-neoadjuvant re-SLNB (specialist centres only) After chemotherapy Specialist technique SPIO = superparamagnetic iron oxide. ICG = indocyanine green. All variants aim to identify the first-draining node accurately. Post-neoadjuvant SLNB (specialist MDT only): requires 3 nodes + clip marking of originally positive node to reduce false-negative rate. Dual tracer remains the UK standard (NICE NG101). Non-radioactive techniques avoid nuclear medicine logistics. ACOSOG Z0011 changed practice: well-selected patients with 1–2 positive nodes in BCS + RT avoid ALND. FIG 06 Key Statistics >95% sentinel node detection rate [1] Krag et al. Lancet Oncol 2010 <5% vs 15–25% lymphoedema: SLNB vs ALND [2] Fleissig et al. Lancet 2006 ALND avoided in 1–2 pos nodes (Z0011) [3] Giuliano et al. JAMA 2017 ~5–10% false-negative rate [4] Kim et al. Am J Surg 2006 FIG 07 References 1. Krag DN et al. NSABP B-32 SLNB trial. Lancet Oncol 2010;11:927. 2. Giuliano AE et al. ACOSOG Z0011 10-year results. JAMA 2017;318:918. 3. NICE NG101. Early and locally advanced breast cancer. 2023. 4. Kim T et al. Lymphatic mapping and SLNB review. Am J Surg 2006. 5. Fleissig A et al. Morbidity after SLNB vs ALND. Lancet 2006;367:1631. Clinically authored by Dr Fiona Tsang-Wright , FRCS (Gen Surg) GMC 4549831 · ORCID 0000-0003-4801-026X
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Definition
A sentinel lymph node biopsy is an operation to remove the first one or two lymph nodes that drain the breast, to check whether breast cancer has started to spread beyond the breast itself.

Common questions The questions patients ask first

Is sentinel lymph node biopsy done at the same time as breast surgery?
Yes, almost always. In most cases the sentinel lymph node biopsy is performed immediately before or after the breast operation itself, under the same general anaesthetic. Occasionally, it is done as a separate operation — for example, if the cancer diagnosis was made from a different procedure.
What happens if cancer is found in the sentinel node?
The next step depends on how many nodes are involved and how much cancer is present. Options include further surgery to remove more nodes (axillary clearance), radiotherapy to the armpit, or, sometimes, no further armpit surgery — the decision is made at a multidisciplinary team meeting with input from oncology12.
What is the risk of lymphoedema after sentinel lymph node biopsy?
The risk is substantially lower than after full axillary clearance — around 1 in 20 vs around 1 in 53. Most patients do not develop lymphoedema; a smaller group does, and it is usually milder than after a full clearance. Any arm swelling, heaviness, or tightness should be reported so it can be assessed early.
Why is the dye blue?
The blue dye (methylene blue or patent blue) makes the sentinel node and the lymphatic channels leading to it easier for the surgeon to see during the operation. The colour may show in the skin, urine, or breast for a day or two — this is harmless.

A sentinel lymph node biopsy is an operation to remove the first few lymph nodes (usually one to four) that drain the breast, to check whether breast cancer has started to spread beyond the breast itself.

The sentinel node is the first lymph node (or small group of nodes) that fluid and cells from a breast tumour would reach. If cancer is going to spread to the lymphatic system, the sentinel node is where it would show up first. Removing and examining this node under a microscope is a reliable way to check whether the cancer has spread, without having to remove all the nodes in the armpit.

Orientation Why you might be reading about this

Sentinel lymph node biopsy is a standard part of surgery for most patients with early invasive breast cancer. Its purpose is to give the most accurate picture of whether cancer has spread, while sparing patients the higher side-effect burden of removing all the lymph nodes in the armpit (a full axillary clearance). Understanding what the operation does and what the results mean helps you follow the rest of the treatment discussion.

Related terms: Axillary lymph node dissection · Lymphoedema · Radioactive tracer · Blue dye · Axilla · Metastasis

The procedure How the operation works

Before or during surgery, the surgeon injects two markers into the breast — a small amount of radioactive tracer (usually technetium-99) the day before or on the day of surgery, and a blue dye during the operation itself4. Increasingly, UK units use a magnetic tracer (SPIO / Magtrace) as a non-inferior alternative that avoids the radioactive logistics5. The lymphatic channels carry these markers from the breast to the first few sentinel lymph nodes in the armpit (usually one to four) — the sentinel nodes. These are the nodes the surgeon then removes through a small separate incision in the armpit.

The removed nodes are examined under a microscope by a pathologist. If no cancer cells are found, no further lymph-node surgery is usually needed1. If cancer cells are found, the next step depends on how many nodes are involved and how much cancer is in them — options include further lymph-node surgery (an axillary clearance) or radiotherapy to the armpit12.

Why it matters Why the sentinel-node approach matters

Before sentinel lymph node biopsy became standard, surgery for breast cancer usually included removal of most of the lymph nodes in the armpit. That operation gave accurate staging information but carried a significant risk of lymphoedema — long-term swelling of the arm caused by damage to the lymphatic drainage. Sentinel lymph node biopsy reduces the risk of lymphoedema substantially, because far fewer nodes are removed (around 5% lifetime risk after SLNB vs roughly 20–25% after axillary clearance)3, while giving equivalent staging information1.

Side effects Side effects and risks

Most patients have only minor discomfort and a small scar in the armpit. Specific side effects to be aware of include:

  • Blue dye — the skin, urine, and sometimes the breast remain faintly blue or green for 24 to 48 hours after surgery4. It is not harmful.
  • Radioactive tracer — the dose is very small; it is the same class of tracer used routinely in diagnostic imaging, and patients are safe to go home the same day.
  • Lymphoedema — the risk is much lower than after an axillary clearance, but it is not zero3. Any swelling, heaviness, or change in arm sensation should be reported so it can be assessed and treated early.
  • Numbness or altered sensation in the upper inner arm, which is usually temporary.
  • Seroma — a collection of fluid under the armpit wound, which usually settles on its own or is drained if troublesome.

At consultation Questions to take to consultation

Good questions for your surgeon include: will my sentinel node biopsy be done at the same time as my breast operation or separately; which tracer do you use; what happens if cancer is found in the node; and what is the rough risk of lymphoedema in your practice. You can read more on the breast cancer surgery page.


Resources Further reading

Sources & guidance

Every figure on this page is anchored to a published source. Tap a number in the text or below to jump to the reference.

  1. rct 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 randomised clinical trial. JAMA. 2017 ;318(10):918–926 doi:10.1001/jama.2017.11470 Cited for: SLNB as standard staging procedure; axillary clearance not required for selected patients with limited sentinel-node involvement.
  2. rct Donker M, van Tienhoven G, Straver ME, et al. (AMAROS investigators). 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. The Lancet Oncology. 2014 ;15(12):1303–1310 doi:10.1016/S1470-2045(14)70460-7 Cited for: Axillary radiotherapy as alternative to axillary clearance for positive sentinel node — comparable disease control with significantly lower lymphoedema rate.
  3. meta analysis DiSipio T, Rye S, Newman B, Hayes S. Incidence of unilateral arm lymphoedema after breast cancer: a systematic review and meta-analysis. The Lancet Oncology. 2013 ;14(6):500–515 doi:10.1016/S1470-2045(13)70076-7 Cited for: Lymphoedema risk after SLNB ~5%; substantially lower than after axillary clearance (~20%).
  4. guidance Association of Breast Surgery (ABS). Best Practice Guidelines: surgical management of breast cancer. London: ABS. 2022 https://www.nice.org.uk/guidance/ng101 Cited for: UK practice for SLNB: tracer methods (radioisotope, blue dye, increasingly magnetic SPIO/Magtrace), same-anaesthetic timing, MDT review of positive nodes.
  5. cohort Karakatsanis A, Christiansen PM, Fischer L, et al. (SentiMag trial collaborators). The Nordic SentiMag trial: a comparison of super paramagnetic iron oxide (SPIO) nanoparticles versus Tc99 and patent blue in the detection of sentinel node (SN) in patients with breast cancer and a meta-analysis of earlier studies. Breast Cancer Research and Treatment. 2016 ;157(2):281–294 doi:10.1007/s10549-016-3809-9 Cited for: Magnetic SPIO tracer is non-inferior to standard radioisotope-plus-blue-dye for sentinel-node identification — context for the magnetic alternative now used in many UK units.