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.
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.
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:
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.
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:
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.