Sentinel lymph node



A sentinel lymph node is the first lymph node or group of nodes to which cancer cells are most likely to spread from the primary tumour. Lymph nodes are small, bean-shaped structures that are part of the lymphatic system, which helps the body fight infection and disease. The sentinel lymph node acts as a kind of “gateway,” filtering fluid that drains from the area around a tumour. If cancer cells start to move away from the main tumour, they will often travel to the sentinel lymph node first.

Where are sentinel lymph nodes found?

Sentinel lymph nodes can be found in different areas of the body depending on the location of the primary tumour. For example, if the tumour is in the breast, the sentinel lymph nodes are usually located in the armpit (axillary lymph nodes). For tumours on the legs, the sentinel lymph nodes may be in the groin. The natural drainage pattern of the lymphatic system near the tumour determines the location of the sentinel lymph nodes.

Why are sentinel lymph nodes important?

Sentinel lymph nodes are important because they help doctors understand whether cancer has begun to spread. By examining the sentinel lymph node, doctors can determine if cancer cells have traveled beyond the original tumour site. This information is crucial for staging the cancer, planning treatment, and predicting a patient’s prognosis.

For some cancers, sentinel lymph node examination is particularly critical. Two common examples include:

  • Invasive ductal carcinoma of the breast: This is the most common type of breast cancer. During surgery for breast cancer, doctors often remove the sentinel lymph nodes to check for cancer cells. If cancer is found in the sentinel nodes, it may mean that the cancer has spread, which could change the treatment plan. If no cancer is found, it’s less likely that the cancer has spread to other parts of the body, and additional lymph nodes may not need to be removed.
  • Melanoma: This is a type of skin cancer that can spread to other parts of the body. The status of the sentinel lymph node is one of the most important factors in determining the stage of melanoma and the need for further treatment. If the sentinel lymph node is free of cancer, it often indicates that the melanoma has not spread to other areas, which can influence the decision for additional therapy.

How do doctors identify sentinel lymph nodes?

Doctors identify sentinel lymph nodes using a procedure called sentinel lymph node biopsy. Before surgery, a small amount of radioactive substance and/or a blue dye is injected into the area around the tumour. These substances travel through the lymphatic vessels to the lymph nodes. The sentinel lymph nodes are the first nodes to absorb the dye or radioactive material.

During the surgery, doctors use a special device that detects radioactivity to locate the sentinel lymph nodes. If blue dye was used, the lymph nodes would be visibly blue, making them easily identified. The sentinel lymph nodes are then removed and sent for examination by a pathologist.

How do pathologists examine sentinel lymph nodes and how may the results be described?

Once the sentinel lymph nodes are removed, a pathologist examines them under a microscope to look for cancer cells. The pathologist may use special staining techniques such as immunohistochemistry (IHC) to highlight any cancer cells that might be present. The examination of sentinel lymph nodes can provide detailed information about whether and to what extent cancer has spread. The results are typically described in the following ways:

  • Negative: No cancer cells are found in the sentinel lymph nodes. This result suggests that the cancer has not spread to these nodes or beyond, which can be a positive sign for the patient’s prognosis.
  • Positive: Cancer cells are found in the sentinel lymph nodes, which means that the cancer has started to spread from its original location. Cancer cells in a lymph node are called a metastasis. The pathologist will usually describe how much cancer is present, whether it’s isolated cancer cells, small clusters, or larger areas of cancer (also known as micrometastases or macrometastases). The extent of spread in the sentinel lymph nodes can help doctors decide on further treatment, such as additional surgery, radiation, or chemotherapy.

About this article

Doctors wrote this article to help you read and understand your pathology report. Contact us if you have questions about this article or your pathology report. For a complete introduction to your pathology report, read this article.

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