Sentinel lymph node biopsy: the complete step-by-step guide

A sentinel lymph node biopsy is a small operation that checks whether breast cancer has spread to the lymph nodes in the armpit. The sentinel nodes are the first few nodes that fluid from the breast drains into, so if cancer cells have travelled, these are the most likely place to find them. Before or at the start of surgery, a small amount of radioactive tracer, a blue dye, or both are injected into the breast near the nipple or tumour. Over a short time these travel through the lymph channels to the sentinel nodes. During the operation, usually done at the same time as a lumpectomy or mastectomy, the surgeon makes a small cut in the armpit, uses a handheld probe to find the nodes giving off a signal and looks for nodes stained blue. Usually only a few nodes are removed. They are sent to the laboratory, sometimes checked during the operation, and fully examined over the following days. If the sentinel nodes are clear, most people do not need more nodes removed. This approach causes far less arm swelling, numbness and stiffness than removing all the armpit nodes. Most people go home the same day or the next day, and recovery from the armpit wound is usually quick.

It finds the first nodes

Checking the first nodes in the drainage path shows whether cancer has reached the armpit.

Only a few nodes are removed

Most people have between one and three nodes taken, sometimes a few more.

Side effects are usually mild

Arm swelling is much less common than after full armpit clearance.

This is a reliable test, but no test is perfect, and it helps to know its weak points.

A small number of results are missed

Occasionally cancer is present in other nodes even when the sentinel nodes look clear. Using both tracer and dye, and removing enough nodes, keeps this uncommon.

The node is sometimes not found

In a small number of people the tracer or dye does not reach a node. The surgeon may then remove some armpit nodes to check them.

Results can take time

The final report on the nodes may take several days, so the plan after surgery is confirmed at a later visit.

What this page cannot tell you

It cannot say whether your nodes will be clear, or which method your surgeon will use. Your team will explain that.

Recovery from the armpit wound itself is usually quicker than recovery from the breast operation done alongside it.

Blue colour for a while

If blue dye was used, your urine may look blue or green for a day or two, and the breast skin may stay faintly blue for weeks or months.

Armpit soreness and numbness

The armpit and inner upper arm may feel sore, tight or numb. This usually settles over weeks, though a small patch of numbness can last.

Gentle arm exercises

Your team will show you simple shoulder movements to keep the arm from stiffening. Start them as advised.

Results appointment

The node results, together with the breast tissue report, decide whether further treatment is needed.