Sentinel Node Biopsy
What is a Sentinel Node?
The sentinel nodes are the first lymph nodes in the armpit to which cancer cells are most likely to spread from new cancer in the breast.
What is a Sentinel Lymph Node Biopsy (SLNB)?
A sentinel lymph node biopsy (SLNB) is a procedure in which the sentinel lymph nodes are identified, removed, and sent for pathological examination to detect the presence of cancer cells. It is thought that if breast cancer cells were to escape into the lymphatic system, they would travel to the sentinel nodes before moving on to other areas.
SLNB is a minimally invasive technique and is proven to be reliable and accurate. During a sentinel lymph node biopsy, the surgeon removes only a few sentinel lymph nodes.
Dissection of the sentinel nodes reduces the possibility of long term side effects such as swelling in the arm and in most cases, provides the necessary information about the cancer. If the sentinel nodes are free of cancer, it can be assumed that the remaining nodes are also clear and no further lymph nodes are then removed.
What Are the Lymph Glands/Nodes?
The lymphatic system is a structure of lymph vessels and lymph glands throughout the body which plays an important role in the body's mechanism of fighting infections and tumours. Tiny channels carry fluid and debris to the lymph nodes/glands which act as filters. Groups of lymph nodes are in the neck, underarms, chest, abdomen, and groin. The lymph nodes that filter waste fluid and cells from the breast are mainly located in the armpit (also called the axilla.) These lymph nodes are usually the first ones affected if cancer spreads beyond the breast. The number of lymph nodes in the axilla varies from person to person but usually ranges from around 10 to 30.
Why is it Important to Know Whether Tumour Cells are Present in the Glands Under the Arm?
The treatment plan for breast cancer is based on whether the lymph glands contain tumour cells.
How is the Sentinel Lymph Node Identified at the surgery?
The following guides the surgeon to identify the sentinel lymph nodes:
- Sentinel Node Imaging is a sophisticated lymphatic mapping that will be performed the day before or the day of surgery. A small amount of radioactive substance is injected into the breast that flows to the sentinel nodes through the lymphatic ducts and can be seen on a nuclear medicine scan (lymphoscintigram). Lymphoscintigraphy is used to find the sentinel lymph nodes which are then removed and checked for tumour cells.
- Blue Dye Injection: Under general anaesthesia, a blue dye is injected into the breast. The dye flows through the lymphatic ducts to the lymph nodes. The first lymph nodes to receive the dye are removed and viewed under a microscope to detect for cancer cells. It may not be necessary to remove more lymph nodes if the cancer cells are not found.
- Gamma probe detection: An intra-operative gamma probe (a highly directional Geiger counter) used in the operating room directs the surgeon to the radioactive isotope injected several hours before the surgery. The radioactive sentinel nodes are removed by the surgeon and investigated for cancer cells.
Not necessarily all the lymph nodes that are mapped contain cancer cells. Rather, they are the first lymph nodes likely to be affected if cancer cells have escaped into the lymphatic system
Does Sentinel Node Biopsy Indicate if I Need further Surgery?
Sentinel node biopsy will not affect whether your tumour is suitable for lumpectomy (wide local excision) or mastectomy but can influence if further surgery to the axilla/armpit is required.
When is Sentinel Node Biopsy Performed?
Sentinel node biopsy is usually performed along with other breast surgeries. Rarely, it is done as a separate procedure before mastectomy when immediate reconstruction is preferred. A final pathological report of the sentinel nodes can allow for a complete axillary clearance at the time of breast surgery/reconstruction. Based on the status of the sentinel nodes, one can decide about the post-surgery radiation which in turn influences reconstruction decision.
What is a False-Negative Result?
In some patients, the cancer cells are not seen in the sentinel lymph nodes although they are present and may have already spread to other regional lymph nodes or other parts of the body. A false-negative biopsy result gives the patient and the doctor a false sense of security about the extent of cancer in the patient’s body.
False-negative SNB results may harm the treatment outcome for various reasons: missed nodes might lead to axillary recurrence that can be difficult to treat, diseased axillary nodes may be a possible source of distant metastases, and under staging affects decisions about systemic and specific radiation therapy to the breast, chest wall and nodal basins.
Sometimes, cancer cells may block the lymphatic vessels running to the lymph nodes that contain cancer cells and result in a false-negative report. In this case, the radioactive substance flows and stains the normal lymph nodes. A false-negative result can be avoided by removing the abnormal palpable nodes (not stained) during the surgery.
Multiple sentinel nodes are present in most breast cancer patients, and it is now accepted that cancer cells often drain directly to a group of nodes rather than to a single node.
Removal of sentinel lymph nodes is based on cherry-picking technique preserving the axillary lymphatics in areas away from the sentinel nodes.
