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Sentinel Lymph Node Biopsy

  • A procedure to remove and check the first lymph node where cancer would be expected to spread
  • Removes fewer lymph nodes to see how far cancer has spread, lowering risk of lymphedema
  • Knowing the number of lymph nodes that contain cancer will help doctors determine treatment
  • Involves breast center, surgical oncology


Our immune system functions as our body’s military force, defending us against infection and other diseases. Lymph vessels and lymph nodes are on the front lines of this system.

Lymph vessels transport a clear fluid called lymph throughout the body. The purpose of lymph fluid is to clean the body’s cells and to provide them with the oxygen and nutrients they need to survive.

Lymph nodes are small, round organs that filter harmful substances collected from the cells, such as bacteria and viruses, from the lymph fluid. If one of these invaders is found, the body triggers a response to take it down.

Groups of lymph nodes are located throughout the body, particularly in the underarms, neck, chest, abdomen and groin.   

When a surgeon operates to remove a cancerous tumor, especially in breast cancers and melanoma, what’s called a “sentinel lymph node” may also be removed to determine whether the cancer has begun to spread.

“Before the use of sentinel lymph node biopsy for early-stage breast cancer, surgeons routinely removed most of the nodes from the axilla or armpit,” explains Brigid Killelea, MD, MPH, section chief of breast surgery at Yale Medicine. Removal of multiple nodes carries a higher risk of arm swelling, which is known as lymphedema, she notes. Typically, the sentinel lymph node procedure involves removal of one to three lymph nodes. “The rate of lymphedema with sentinel node biopsy is low, typically 5% or less,” says Dr. Killelea.

What is a sentinel lymph node?

For people with cancer, lymph nodes play another key role—they can be used to determine whether cancer has become metastatic, meaning it’s begun to spread from the original tumor site to other parts of the body. (The word “sentinel” means to stand watch.)

The sentinel lymph node is the first node where the cancer would be expected to spread, given the flow of the body’s lymphatic system. Some cancers spread via the blood and others, like breast cancer and melanoma, typically spread first to lymph nodes. In a procedure called sentinel lymph node biopsy, a surgeon removes the first node that drains the breast to check for metastasis. If that node is clear, meaning there are no cancer cells in it, then the larger surgery can be avoided.

What happens during sentinel lymph node biopsy?

Sentinel lymph node biopsy is often performed during the operation to remove the main tumor, but it can also be done as a separate procedure.

The surgeon identifies the sentinel lymph node by injecting a radioactive substance or blue dye (or both) near the tumor site. Then, the surgeon uses a device to detect radioactivity in the nodes or looks for nodes that are stained blue. Once the sentinel node is identified, the surgeon makes a small incision and removes the node. Then, a pathologist analyzes it under the microscope for cancer cells.

Overall, the procedure takes about half an hour. 

What do the biopsy results mean?

If the biopsy is positive, it means that cancer cells have been found in the sentinel lymph node. The surgeon may then proceed with axillary lymph node dissection—a more invasive procedure that involves removing more lymph nodes.

For certain types of cancer, biopsy results are also used to determine the cancer stage. The American Joint Committee on Cancer has developed the “TNM” staging system, which considers three features of the cancer: the size of the main tumor (T), the number of affected lymph nodes (N) and the presence of metastasis (M). Doctors can use the cancer stage to guide treatment.

If the biopsy is negative, the cancer is unlikely to be metastatic, and no further lymph node surgery is needed.

Are there any side effects from the biopsy?

Since lymph vessels are cut during the biopsy, lymph fluid can sometimes accumulate in that area, causing a seroma (a pocket of fluid). Any time lymph nodes are removed from the axilla there is also a risk of lymphedema. This can be an ongoing problem, but physical therapy and other treatments can help. Patients may also experience loss of sensation and decreased range of motion in the area.

What makes Yale Medicine’s approach to sentinel lymph node biopsy unique?

The sentinel lymph node biopsy for breast cancer is routinely performed by Yale Medicine breast surgeons, who are all experts in this technique, at Yale Cancer Center’s Breast Center, located at Smilow Cancer Hospital. 

“The management of the axillary lymph nodes for early-stage breast cancer patients has continued to evolve,” says Dr. Killelea. “And these days patients who are undergoing lumpectomy can sometimes avoid axillary dissection—even if they have one or two lymph nodes with cancer. I would encourage patients to discuss the sentinel node biopsy and need for additional surgery with their breast surgeon.”