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• What is a Sentinel Lymph Node?
• What is Sentinel Lymph Node Biopsy?
• How is Sentinel Lymph Node Biopsy Performed?
• Why is Sentinel Lymph Node Biopsy Performed?
• What Happens When the Sentinel Lymph Node is Found to Be Cancerous?
• What Are the Side Effects of a Sentinel Lymph Node Biopsy?
• Is Sentinel Lymph Node Biopsy Accurate?
• Are All Breast Cancer Patients Candidates for Sentinel Lymph Node Biopsy?
• Additional Resources and References

What is a Sentinel Lymph Node?

Courtesy of Tyco Healthcare Group.

In the breast, a network of lymphatic vessels drain fluid and cells to the bean-shaped lymph nodes in the axilla (armpit). The “sentinel” node is the very first lymph node(s) to receive drainage from a cancer-containing area of the breast.

Put another way, when breast cancer cells begin to escape from the primary tumor site in the breast they travel to the lymph nodes under the arm; the first lymph node they reach is the 'sentinel' lymph node.

What is Sentinel Lymph Node Biopsy?

When breast cancer is diagnosed, women (and men) must often undergo axillary lymph node dissection (i.e., removal of underarm nodes) to check for the spread of cancer. This process is part of “staging” the cancer. Unfortunately, the removal of these lymph nodes can lead to lymphedema (chronic swelling) of the arm in a certain percentage-- about 10-20%--of cases.

Sentinel lymph node biopsy is a diagnostic procedure used to determine whether breast cancer has spread (metastasized) to axillary lymph nodes (i.e., lymph glands under the arm).  A sentinel lymph node biopsy requires the removal of only one to three lymph nodes for close review by a pathologist.  If the sentinel nodes do not contain tumor (cancer) cells, this may eliminate the need to remove additional lymph nodes in the axillary area.

Research on this technique has shown that sentinel lymph node biopsy may be associated with less pain and fewer complications than standard axillary dissection. However, the procedure may not be appropriate for all breast cancer patients.

How is Sentinel Lymph Node Biopsy Performed?

Sentinel lymph node biopsy is a complex surgical procedure that requires an experienced surgeon to successfully perform. Before going to the operating room, the surgeon injects a small dose of a low-level radioactive tracer called technetium-99 into the breast in the region of the patient’s tumor. Technetium-99 contains less radiation than a standard x-ray, CT scan or bone scan and is a relatively safe substance.  A blue dye is also injected to help visually track the location of the sentinel node during surgery. The surgeon then uses a hand held counter to detect the radioactive tracer and locate the sentinel node.

Sometimes, nuclear medicine images (also known as lymphoscintigraphy) of the lymphatic system will be obtained after injecting the technetium-99 before surgery.  Since the uptake of the technetium-99 by cancerous lymph nodes is sometimes different than the uptake by normal lymph nodes, these nuclear medicine images may also help show which lymph nodes are cancerous.

Next, the surgeon will wait for the technetium-99 and dye to travel from the tumor region to the sentinel lymph node(s), just as cancer cells might spread. Depending on the protocol followed, the surgeon usually waits between 45 minutes to 8 hours after injection before bringing a patient to the operating room for the biopsy.  At some point during the procedure, a small amount of blue dye will also be injected into the breast tissue near the area of the tumor.  Once the technetium-99 tracer and dye have reached the nodes, the surgeon will scan the area with an electric, hand-held gamma ray counter (called a Geiger counter) to detect the radioactive technetium-99.

The gamma ray counter is attached to a small probe which the surgeon traces over the axilla to locate the sentinel node(s).  When the radioactive agent is found, the gamma ray counter will emit an audible tone, revealing the exact location of the sentinel node(s). Once the area has been pinpointed, the surgeon will make a small incision (usually one-half inch) and remove the sentinel node(s) for a pathologist to examine under a microscope.  The blue dye provides additional visual confirmation of the sentinel node’s location during surgical removal.  Several clinical trials have revealed that in the vast majority of cases, if the sentinel node does not contain cancer, then the cancer has not spread past the breast.  Sentinel node biopsy does not usually require the placement of a fluid drainage tube (common in axillary node dissection).

Why is Sentinel Lymph Node Biopsy Performed?

Courtesy NIH/NCI

Sentinel lymph node biopsy may help in determining which patients can avoid axillary node dissection and the removal of 10 to 30 lymph nodes.  Most patients have only one to three sentinel lymph nodes under the arm.  Thus, an average of only two lymph nodes are removed in each patient with a sentinel node biopsy.  This, in turn, may reduce post-operative complications.  A standard axillary node dissection, removal of the underarm lymph nodes, usually requires a larger four to six inch incision and a longer recovery period than a sentinel node biopsy.
Researchers are currently investigating whether sentinel node biopsy should routinely be performed in place of axillary node dissection. However, surgeons caution that more studies on the benefits and risks of sentinel node biopsy should be conducted before the procedure becomes widespread.  Typically, patients who undergo a modified radical mastectomy or a lumpectomy may require lymph node removal.  Sentinel node biopsy or axillary node dissection helps surgeons determine if breast cancer has spread to the lymphatics and the extent of the spread. 

In a study published in The New England Journal of Medicine, 443 patients at 11 medical centers across the United States underwent sentinel node biopsies. Researchers discovered that if the gamma ray counter detected the radioactive agent (technetium-99) in the patients, then the sentinel node biopsy was 97% accurate in pinpointing all cancerous lymph nodes.  However, the study was not completely successful. The gamma ray counter missed cancerous nodes in 13 of the 114 women whose cancer had spread past the breast.  In an upcoming study, researchers at the National Cancer Institute will compare sentinel node biopsy to the standard method of lymph node removal (axillary node dissection) on 4000 women to determine which procedure is superior.

What Happens When the Sentinel Node Is Found To Be Cancerous?

After the surgeon removes the sentinel node(s), a pathologist will perform a preliminary examination of the nodes to determine whether they contain cancer cells. The sentinel lymph nodes will be classified as negative (no cancer), positive (contain cancer), or indeterminate.  However, this preliminary report is followed by close examination and the final pathology report.

If the sentinel node is determined to be cancerous while the patient is still in surgery, the surgeon will usually remove additional lymph nodes in the axilla.   However, the final pathology report is not available until after the surgery has been completed, and patients should schedule a follow-up visit with the surgeon to discuss the final report.  Sometimes, the final report indicates a positive (cancerous) sentinel node that was not seen on preliminary review.  If this occurs, then additional surgery may be necessary to remove more nodes for examination.

What Are the Side Effects of a Sentinel Lymph Node Biopsy?

Because sentinel lymph node biopsy involves removal of fewer lymph nodes than a standard axillary lymph node dissection, the potential for side effects such as lymphedema is much lower. Many patients who undergo sentinel node biopsy do not experience any side effects. However, some patients report post-operative pain, nerve damage, or lymphedema after the procedure. These symptoms occur more frequently when additional lymph nodes are removed along with the sentinel node.

The blue dye that is injected will turn the urine green for about 24 hours and may cause a temporary bluish discoloration of the breast skin. The radioactive energy from the technetitum-99 injection dissipates on its own, and some of the radiation is eliminated through urine or bowel movement. The result is that the radioactive material is only in the patient for a short time. Once the energy is eliminated, patients will no longer carry the radioactivity. The levels of radiation involved in a sentinel node biopsy are considerably lower than a patient would receive in a conventional x-ray study, bone scan or CT scan.

Most women who undergo sentinel node biopsy spend one day or less in the hospital. Occasionally, sentinel node biopsy may be performed on an outpatient basis.

Is Sentinel Node Biopsy Accurate?

Many surgeons agree that breast cancer may be accurately staged without having to remove any lymph nodes besides the sentinel node. Nevertheless, researchers are finding that a low percentage of sentinel node biopsy results can turn out to be “false negatives.”  That is, the sentinel nodes do not contain cancer when, in fact, the patient’s other axillary lymph nodes do contain cancer. 

This has been an important teaching point in many advanced courses presented to physicians who perform sentinel node biopsy.  If a physician is uneasy about the looks of a sentinel node, even though it is not cancerous, the surgeon will typically remove additional lymph nodes to check their status.

The scenario of a negative (non-cancerous) sentinel node and positive (cancerous) additional nodes in a patient can occur for several reasons, including:

• The timing of the dye injections
• The type of dye/tracers used
• The presence of more than one sentinel node
• The way in which the initial node was sectioned or stained in the pathology lab

The American College of Surgeons Oncology Group recommends that physicians perform at least 30 sentinel lymph node biopsies followed by complete axillary node dissection, with an 85% success rate in identifying the sentinel lymph node(s) and a 5% or lower false positive rate. After they have accomplished this, physicians can then perform sentinel lymph node biopsy without a back-up axillary node dissection. According to the Canadian committee, physicians who have performed less than 30 sentinel lymph node biopsies should only perform the procedure as part of a clinical trial. Patients who are considering sentinel lymph node biopsy should ask their surgeon how many procedure he/she has performed and his/her success rate.

The committee also recommended that all patients be fully aware of the potential benefits and challenges of sentinel lymph node biopsy, including what is known and not known about the procedure. In particular, patients should be aware that there is a small chance (usually less than 10%) that the results of the sentinel lymph node biopsy can be inaccurate (false negatives); that is, there is no cancer in the sentinel nodes but cancer exists in other axillary lymph nodes. Missing these cancer cells can affect a patient's treatment after surgery and the chances that breast cancer may return.

To address some of the challenges of sentinel lymph node biopsy, the committee recommended guidelines for both physicians and patients:

• Sentinel lymph node biopsies should only be performed by experienced physicians who have first familiarized themselves with literature on the procedure, have established a protocol for all aspects of the procedure, and have successfully performed back-up axillary node dissections on a sufficient number of patients.
• Surgeons who do not often perform breast cancer surgery should not perform sentinel lymph node biopsy.
• If a “positive” (cancerous) sentinel lymph node is found, a full axillary node dissection should be performed.

The report of the steering committee of Health Canada's Canadian Breast Cancer Initiative was published in the July 24, 2001 issue of the Canadian Medical Association Journal. Click here to learn more about this report.

More recently, several studies have been published further suggesting that sentinel lymph node biopsy may be a promising advance in breast cancer surgery. In a small study published in 2003 in the The New England Journal of Medicine, researchers found that sentinel lymph node biopsy missed cancerous cells in only 9% of cases, and in most of these instances, the women did not develop a new cancerous tumor. Women who underwent sentinel lymph node biopsy also experienced less arm pain and better mobility compared to women who underwent standard axillary lymph node dissection.

In a June 2005 study published in the Journal of Clinical Oncology, British researchers found that women who underwent sentinel lymph node biopsy experienced significantly less arm swelling and numbness compared to women who under standard lymph node removal.

Are All Breast Cancer Patients Candidates for Sentinel Lymph Node Biopsy?

Not all women with operable breast cancer who have been recommended to have some of their axillary (armpit) lymph nodes removed are candidates for sentinel node biopsy. According to a steering committee of Health Canada's Canadian Breast Cancer Initiative, the following women are poor candidates for sentinel lymph node biopsy:

• Women with palpable (able to be felt) lymph nodes
• Women with locally advanced breast cancer
• Women with multi-focal breast cancer (cancer in many areas of the breast)
• Women who have previously undergone breast surgery (including breast reduction)
• Women who have previously undergone radiation therapy to the breast

Moreover, the American Cancer Society states that sentinel lymph node biopsy is most suitable if there is a single tumor less than 5 centimeters across in the breast, no prior chemotherapy or hormone therapy has been given, and the lymph nodes do not feel enlarged.

Women should discuss the benefits and risks of sentinel lymph node biopsy with their cancer treatment team.

Additional Resources and References

• The American Cancer Society provides information on sentinel node biopsy at http://www.cancer.org/
• The January 26, 2006 Imaginis report, Another Study Finds Removing Fewer Lymph Nodes Effective At Reducing Side Effects of Breast Cancer Surgery," is available at http://www.imaginis.com/breasthealth/news/news1.26.06.asp
• The October 20, 2003 Imaginis report, Study Supports Removal of Fewer Lymph Nodes in Breast Cancer Patients," is available at http://www.imaginis.com/breasthealth/news/news10.20.03.asp
• The August 1, 2001 Imaginis report, "Canadian Report Outlines Benefits and Challenges of Sentinel Lymph Node Biopsy," is available at http://www.imaginis.com/breasthealth/news/news8.01.01.asp

Updated: January 31, 2008

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