What Is the Sentinel Lymph Node in Breast Cancer?

The first nodes in the axilla affected by breast cancer are known as sentinel or guardian lymph nodes. A positive sentinel lymph node biopsy or SLNB indicates that the cancer is no longer in situ.

Breast cancer can spread to other parts of the body. It first reaches the lymph nodes in the armpit (axilla) close to the breast. Lymph nodes drain a liquid called lymphatic fluid from the breast and arm. The first nodes in the axilla affected by breast cancer are known as sentinel or guardian lymph nodes. If the doctor suspects that cancer has spread to sentinel lymph nodes or adjacent nodes, the physician may recommend a sentinel lymph node biopsy.

A positive sentinel lymph node biopsy or SLNB indicates that the cancer is no longer in situ. Cancer has spread to the sentinel lymph nodes and probably to other nearby lymph nodes. Thus, SLNB helps the physician to determine the exact stage of cancer that would help them to develop a treatment plan.

If the SLNB shows cancerous cells in three or more sentinel lymph nodes, the physician may recommend axillary dissection. There are three levels of axillary lymph nodes, which correspond to  options for dissection:

• Level I: This refers to removing all tissue below the axillary vein and extending to the side where the axillary vein crosses the tendon of a muscle called the latissimus dorsi.
• Level II: This includes removing lymph nodes present under the chest wall muscles called the pectoralis minor.
• Level III: This includes complete removal of nodes present above the pectoralis minor muscle.

Axillary dissection is a surgical procedure that involves opening the axilla to identify, examine or remove the lymph nodes. It has been the standard technique used for the treatment of breast cancer affecting the axilla.

SLNB has two parts

• Lymphatic mapping
• Surgical procedure

Lymphatic mapping or lymphoscintigram involves injecting radioactive dye into the skin around the site of the tumor. Next, the physician uses a special camera to locate the radioactive material because it travels from the original tumor site to the sentinel lymph nodes.

After completing the lymphatic mapping, the physician injects a second blue dye to visualize the lymph nodes, which are already located by the specialized camera. The physician removes the sentinel lymph nodes and sends them for examination.

The surgical biopsy procedure includes a wide local excision, where the physician removes the tumor along with the biopsy tissue and some normal tissue surrounding it.

After examination of the biopsied tissue, the sentinel lymph node may show evidence of a cancerous tumor. If sentinel lymph nodes don’t show any cancer, it is improbable that cancer has spread to the remaining lymph nodes and no further surgery is needed.

The complications of SLNB include

• Numbness
• Pain
• Bruising
• Seroma (fluid buildup in the biopsied area)
• Thickening or hardening of the skin at the biopsy site
• Allergic reaction to blue dyes
• Infection

The axillary dissection is performed simultaneously during a mastectomy surgery and is usually carried out under general anesthesia. The surgeon makes an incision under the arm and removes 10 to 40 lymph nodes from level I and II. Usually, the surgeon does not remove level III axial lymph nodes. However, the formation of lumps or larger nodes may force the surgeon to remove the level III lymph nodes as well. Finally, the surgeon places a small tube in the area and closes the incision with stitches or staples. A drainage bag attached to the end of the tube helps collect fluid discharge.

Some of the complications and side effects of the surgery include

• Signs of infection, such as pain, redness or pus
• Discomfort and soreness around the wound site
• Hematoma (pooling of blood)
• Swelling and bruising over the breast or axilla
• Seroma (fluid accumulation under the skin in the armpit)
• Shoulder stiffness
• Lymphedema (swelling of one of the arms or legs)
• Numb patch on the upper arm