Sentinel Lymph Node Biopsy
If you’ve been diagnosed with breast cancer, your doctor will likely recommend that you have surgery to see if the cancer has spread to your lymph nodes. In a sentinel lymph node biopsy, the surgeon looks for and removes the lymph nodes where lymph from the breast drains first. This surgery can happen at the same time as a lumpectomy or mastectomy, or it can be performed separately.
Why sentinel lymph node biopsy is done
A surgeon performs a sentinel lymph node biopsy to determine if early-stage breast cancer has spread beyond the breast. This information can help doctors determine the stage of the cancer and create a tailored treatment plan.
Cancer is able to spread (metastasize) when a cancer cell breaks free from a tumor and travels through lymph fluid or blood to other organs. Lymph nodes support the lymphatic system by trapping bacteria, viruses, cancer cells, and other unwanted substances and removing them safely from the body.
The dictionary defines “sentinel” as a guard, watchdog, or protector. Likewise, the sentinel lymph nodes are the first nodes “standing guard” for your breast. If cancer cells are breaking away from the tumor and traveling away from your breast via the lymph system, the sentinel lymph nodes are more likely than other lymph nodes to contain cancer.
What to expect during sentinel node biopsy
In order to biopsy sentinel lymph nodes, the surgeon must first locate them. This step is called lymph node mapping (also called lymphatic mapping). You might have lymph node mapping either the day before or the day of surgery.
During lymph node mapping, you’ll be awake as your surgeon injects a blue dye, radioactive liquid, or both under your skin near the tumor site to mark the sentinel nodes. You can ask your doctor to use a local anesthetic to reduce pain from the injection. A special instrument is used to track the radioactive liquid and locate the sentinel nodes.
Once your surgeon can confidently see the sentinel lymph nodes, they can do the biopsy.
During the procedure, you’ll be under anesthesia. The surgeon will make a small incision under the arm and take out the sentinel nodes that have absorbed the injected liquid. They will send the removed nodes to a pathologist, who checks for cancer cells using a microscope.
If you have a sentinel lymph node biopsy separate from breast cancer surgery, you’ll likely be able to leave the hospital that same day.
What happens if a sentinel node biopsy is positive?
If there are cancer cells present in the sentinel lymph nodes, your doctor may recommend the removal of additional lymph nodes in a surgery called axillary lymph node dissection. The doctor may also offer specific treatment recommendations, such as radiation therapy to the lymph nodes.
In 2024, the American Society of Clinical Oncology (ASCO) released a paper recommending that people with cancer in more than two sentinel lymph nodes receive axillary lymph node dissection.
Is sentinel lymph node biopsy right for me?
The type of lymph node surgery a person has depends on the size and other characteristics of the cancer. Some new research suggests the surgery might not be necessary for all people with breast cancer. For instance, one study found that people with breast cancer that's smaller than 2 centimeters may be able to safely avoid lymph node biopsy.
A sentinel lymph node biopsy may make sense for you if you’ve been diagnosed with early-stage, invasive breast cancer that's larger than 2 centimeters and has a low-to-moderate risk of having moved into the lymph nodes.
According to guidelines from the American Society of Breast Surgeons (ASBrS), doctors may recommend a sentinel lymph node biopsy if:
you’ve been diagnosed with invasive breast cancer that can be treated with surgery first
there are two or more breast cancer tumors that have each formed separately from one another (these types of breast cancers are considered rare)
you’ve been diagnosed with DCIS (ductal carcinoma in situ) and have chosen to have or need a mastectomy
you’ve already had breast cancer surgery, lymph node removal surgery, or both
you’ve received treatment such as chemotherapy before breast cancer surgery and your doctor needs to check your lymph nodes
According to the ASBrS guidelines, doctors should not recommend sentinel lymph node biopsy for anyone who has been diagnosed with:
a cancer that is 5 centimeters or larger or locally advanced (meaning the cancer has spread extensively in the breast, to the nearby lymph nodes, or into the chest wall or skin)
inflammatory breast cancer (a rare but aggressive form of breast cancer that causes redness and inflammation in the breast)
DCIS that isn’t large and can be treated with lumpectomy
In 2025, ASCO released a guideline update recommending against sentinel lymph node biopsy for people who are post-menopausal and 50 years old or older, have been diagnosed with hormone receptor-positive, HER2-negative breast cancer that is 2 centimeters or smaller, and will undergo breast-conserving therapy (such as a lumpectomy).
Questions to ask your surgeon
Some people may find it helpful to ask the following questions:
Am I a good candidate for sentinel node dissection? Why or why not?
How frequently do you perform this type of biopsy?
Do you use dye and radioactive liquid to identify the sentinel nodes? Why? Where do you inject the substance — under the skin or into the tumor?
If you can’t see the sentinel nodes, what happens next?
How many sentinel nodes do you typically remove during a sentinel node biopsy?
What happens next if the sentinel lymph nodes have cancer cells present? Do you typically recommend an axillary lymph node dissection, or are there other options I can consider?
— Last updated on August 26, 2025 at 7:33 PM