What is a sentinel lymph node?

Sentinel lymph nodes are a part of the lymphatic system.

The lymphatic system's job is to pick up cellular waste, water, and other substances accumulated between cells. The sentinel lymph nodes are the first to be reached by the lymphatic drainage system, and play an important part in fighting infection and diseases. The sentinel lymph nodes work as a drainage system to help remove waste products and excessive fluid from the body. It is made up of lymph fluid (when excess fluid drains from the body), lymph nodes (small glands which act as filters when lymph fluid drains through them). Sentinel lymph nodes are the first nodes to receive lymph fluid which drains from the breast.

The underarm (axilla) is fundamental in this network that consists of different lymph nodes, and it is the point when the routes of lymphatic drainage branch of the breast. In the case of breast cancer, through these routes, cancerous cells can disseminate to other organs and must pass through the lymph nodes. If the tumour cells haven’t reached the first lymph node, it’s almost certain that other lymph nodes still haven’t been affected.

A lymph node biopsy is carried out when there is a lesion diagnosed as cancerous. Through the biopsy, the specialist can determine if the cancer has spread to other areas of the body. This procedure is usually done at the same time as breast surgery such as a mastectomy (removing the breast), or wide excision (when the cancer is removed along with some healthy tissue around it).

Why is sentinel lymph node biopsy important?

The biopsy or lymphoscintigraphy allows to identify if the cancer has spread to the lymph nodes of the armpit and, thanks to this information, it is possible to establish the best therapy and avoid the elimination of axillary lymph nodes.

The biopsy involves injecting a small amount of radioactive fluid that reaches the first sentinel node, which will then be removed through an incision.

If the cancer has not spread, the tumour has not yet begun to expand and intervention is not required. In case where it is very widespread, the axillary cavity must be emptied. The biopsy can be performed before or during surgery.

The results of the biopsy can lead to different situations:

• The sentinel lymph node does not contain tumour cells.
• The sentinel lymph node contains some isolated tumour cells. In this case, it is removed.
• The sentinel node contains clusters of tumour cells, or macro metastasis (one or more tumour deposits greater than 2m), and there is a risk that other lymph nodes also contain them. The axillary cavity is emptied.

How must you prepare for a lymph node biopsy?

The preparation varies according to the patient and the preferences of the surgeon.

Before the operation you will need to go to the nuclear medicine department of a hospital, where a small amount of a radioactive substance (isotope) will be injected into the breast that is affected. A special camera is used to map the flow of the substance to the lymph nodes.

What is felt during the examination?

When the local anaesthetic is injected, the patient will notice a small pinch and a slight itch. The area of the biopsy will be slightly painful during a few days after the examination. The pain is light and can be controlled easily using painkillers which can be purchased in any pharmacy.

During the healing of the incision, exercise should be avoided, including lifting the weight that can cause pain. It’s important to follow the advice given by the specialist.