A sentinel lymph node is the first lymph node that cancer is likely to spread to from the primary tumor. A sentinel node biopsy is the identification and removal of this lymph node so that it can be examined for cancer cells.

The concept of sentinel lymph node biopsy was proposed in 1960, but it took nearly 40 years for it to come into standard practice. It’s now regularly performed for breast cancer, melanoma, and some other types of cancer.

In this article, we take a deep look at sentinel lymph node biopsies including what you can expect during the procedure and when they’re performed.

A sentinel lymph node is the lymph node that a tumor is most likely to spread to first based on the direction lymph fluid from your tumor is expected to flow. The name comes from the word “sentinel,” which means a soldier standing guard at a point of passage.

The location of a sentinel lymph node depends on the type of cancer you have. For example, the sentinel lymph node for breast cancer tends to be in your armpit, but can also be in your chest if the cancer is near your breastbone.

For melanoma, the location of the sentinel lymph node can depend on where the cancer forms. In some cases, there’s more than one sentinel lymph node.

Doctors identify sentinel lymph nodes by injecting a radioactive substance or special dye near the tumor.

A sentinel lymph node biopsy is when the sentinel lymph node is identified and removed to check whether cancer cells are present. It’s performed after the initial cancer diagnosis and can help doctors stage the cancer.

Cancers that have spread beyond the original tumor are often treated differently than cancers that haven’t spread.

Sentinel lymph biopsies are most commonly used to stage breast cancer and melanoma. They’re also used to stage endometrial cancer and penile cancer.

People with some other types of cancer may also make good candidates for a sentinel lymph node biopsy. Researchers are investigating potential benefits for:

The mainstream use of sentinel lymph node biopsy has drastically changed how breast cancer is managed.

Research has found no difference in survival between women who receive a sentinel lymph node biopsy over a much more invasive procedure called an axillary lymph node dissection, which can involve removing up to 40 lymph nodes.

The benefits of sentinel node biopsy for early stage melanoma remain controversial. Studies have found that it can provide useful prognostic information but can increase the short-term management cost fourfold.

A sentinel lymph node biopsy is usually performed at the same time as your primary tumor removal. Here’s generally what you can expect:

  1. First, your surgeon will attempt to locate your sentinel lymph node. They’ll do this by injecting a radioactive substance or blue dye near your tumor.
  2. Immediately after the injection and again after 1 to 2 hours, they’ll perform a lymphoscintigram or lymphatic drainage scan. This scan allows them to see a road map of how the dye moves through your lymphatic channels and where the dye drains.
  3. Once the lymph node is located, your surgeon will make a small incision to remove the node.
  4. A type of doctor called a pathologist will examine the node for cancer cells in a lab. If they find cancer, you may have more lymph nodes removed in the same procedure or on another day.

You may be able to go home the same day as your procedure, or it may require a short hospital stay.

Potential risks or complications

Like every type of surgical procedure, sentinel lymph biopsy comes with a risk of some complications. Most people have no or mild side effects such as:

  • swelling
  • pain
  • bruising
  • fatigue

If you received blue dye, your urine may change color for the next 24 to 48 hours until the dye can leave your body.

A potentially painful complication of lymph node removal is lymphedema, which is a buildup of lymph fluid that can cause swelling. According to a 2022 study, the chances of developing lymphedema after a sentinel lymph node biopsy is approximately 5%.

In a 2020 study, researchers found that the sentinel node identification rates vary depending on which substance is injected. They found that successful identification rates were:

  • 100% for dual tracers
  • 99.4% for radioisotopes
  • 89.1% for blue dye

A positive result on your biopsy suggests that the cancer has spread to the sampled lymph node and may have spread to other organs or lymph nodes.

A negative result suggests that cancer hasn’t spread from the original tumor to your lymph nodes or organs.

It’s possible to have a false-negative result where cancer cells aren’t seen in the biopsy even though the cancer has spread beyond its original site.

In a 2020 study, researchers found that sentinel lymph node biopsy correctly identified cancer in 91% of node samples in people with lobular carcinoma of the breast.

Older and obese people tend to have more false negatives than people who are younger or aren’t obese.

The next step depends on whether your biopsy result is positive or negative. Either way, your healthcare team can help you determine your treatment options.

If your result is negative, there’s a very low chance that your cancer has spread to other lymph nodes and no further lymph node surgery will likely be needed. You may receive other treatments for the primary cancer such as radiation therapy and chemotherapy.

A positive biopsy might mean that more lymph nodes need to be removed to assess how far the cancer has spread. It also likely means more extensive cancer treatment.

A sentinel lymph node biopsy is a procedure where doctors identify and remove the lymph node that your tumor is most likely to spread to.

A pathologist will examine this lymph node for cancer. If they don’t find evidence of cancer, it’s unlikely that your tumor has spread to any lymph nodes.

Sentinel lymph node biopsy is most often performed in people with breast cancer or melanoma but its potential benefits are also under investigation for many other types of cancer.