Sentinel lymph node biopsy in breast cancer: how it works and what to expect

Breast cancer cells that travel beyond the breast usually pass first to lymph nodes in the armpit. The sentinel node is the first node, or the first few, that the breast drains into. Ashford and St Peter's describes it as the first node in the armpit to which breast cancer can spread, so a node that is clear is a good sign that the nodes beyond it are also clear.

The Bristol leaflet explains why this matters: decisions about further surgery, radiotherapy, hormone treatment and chemotherapy depend partly on whether the nodes contain cancer cells. Examining them gives the team the information needed for staging, which means working out how far the cancer has spread, and for choosing the right treatment plan.

The Bristol leaflet describes sentinel node biopsy as standard for early breast cancer when an ultrasound scan of the armpit before surgery shows no obvious involvement. Your surgeon decides after reviewing your scan results whether this method fits.

The alternatives to a sentinel biopsy are other forms of armpit surgery. A Birmingham breast leaflet names node sampling and node clearance as options alongside sentinel biopsy. Your surgeon recommends the method that fits your scan results and the type of cancer.

The Bristol leaflet says the tracer injection is given on the morning of the operation or sometimes the day before. There are no special preparations beyond those for the main operation, which is usually a general anaesthetic with fasting beforehand.

It is worth asking before the day how the tracer injection feels, since it is given into the breast with a fine needle. Ask also whether you will be given an exercise leaflet, as both leaflets read for this page mention arm exercises as part of recovery.

Two markers are used. A small amount of radioactive material called technetium is injected into the breast and travels along lymph channels to the sentinel nodes. Once you are asleep, a blue dye is also injected, which stains the node. A hand-held probe in theatre detects the tracer and guides the surgeon to the right place.

Through a small cut in the armpit, or through the existing scar if the biopsy is done together with a mastectomy, the surgeon removes the nodes that are radioactive or blue. Ashford and St Peter's says the operation is done under general anaesthetic. The nodes go to a pathologist, who examines them under a microscope.

The blue dye is harmless but noticeable. Urine and stools can look blue or green for a day or two, and tears and contact lenses can be tinted. The breast skin may stay bluish for months, and the Bristol leaflet says rarely longer than a year.

The Bristol leaflet puts the chance of an allergic reaction to the dye at less than 1%, treated by the anaesthetic team, and the leaflet from Ashford and St Peter's says rare reactions can occur under anaesthetic. Other effects include arm stiffness, numbness or tingling near the wound, infection, and a seroma, which usually settles within four to six weeks.

Lymphoedema, a long-term swelling of the arm, is less common after a sentinel biopsy than after a full clearance of the nodes. The Bristol leaflet says it affects fewer than 5 out of 100 people. It also calls the test 95% accurate for staging, so a small proportion of results can be wrong, which is a reason the full cancer results are reviewed by a team.

If the sentinel node is clear, the Bristol leaflet says no further treatment to the armpit is needed. If it contains cancer cells, the team discusses the next step, which may be radiotherapy to the armpit or an operation to remove more nodes, and sometimes a clinical trial option. Results usually come at the follow-up appointment, not on the day.

Recovery from this part of the operation is generally easier than from a full node clearance, with earlier arm movement. The arm exercise leaflet matters here, and the recovery notes in the mastectomy and lumpectomy guides give the wider picture.

Contact your breast care team if the wound becomes red, hot or painful, if you develop a temperature, or if the arm begins to swell. Use NHS 111 out of hours, and 999 for chest pain or sudden breathlessness.