Once the skin biopsy has been done and it has been determined that the patient has melanoma, the next step is to establish whether or not the melanoma has spread beyond the primary tumor or local tissues.
The presence or absence of melanoma cells in the lymph nodes is one of the most important prognostic factors we have. Since it indicates what the melanoma might do in the future as well as the type of treatment you may need.
The Role of the Sentinel Lymph Node Biopsy (SLNB)
Sentinel Lymph Node Biopsy (SLNB) is a specialized procedure done to determine whether any melanoma cells have spread to the sentinel nodes. If the melanoma has spread, it will usually spread to the lymph nodes nearest the area of the primary melanoma.
The sentinel lymph nodes are the first of those lymph nodes to receive drainage from the primary tumor, and therefore the ones most likely to have melanoma cells if any of them have spread.
When a Sentinel Lymph Node Biopsy (SLNB) is Indicated
- Melanoma is equal to or greater than 1.0mm
- Ulcerated tumors of any thickness
- Positive margins
- Lymphovascular Invasion (seeing cancer cells in the lymphatic channels or blood vessels)
- Mitotic rate (the rate at which cells divide) in young adults)
When a Sentinel Lymph Node Biopsy (SLNB) is not Indicated
- Melanomas less than 0.76mm with no other risk features
- It is already known that melanoma is in the lymph nodes (Stage III)
- It has spread to distant organs (Stage IV)
How the Sentinel Lymph Node Biopsy (SLNB) is done
The Sentinel Lymph Node Biopsy (SLNB) has two parts, a radiology test called lymphatic mapping, and a surgical procedure. A wide local excision should also be performed at the same time.
- Lymphatic Mapping (Lymphoscintigram) usually involves injecting radioactive dye into the skin around the site of the original melanoma. Then a special camera is used to watch the radioactive material move from where the melanoma was biopsied to the group of lymph nodes the melanoma is most likely to travel to first. These are called the sentinel nodes and in most patients, there are between 1 and 5 sentinel nodes.
- Surgery is performed after the lymphatic mapping has been completed. You will generally receive a second agent (blue dye) that will help visually identify the lymph nodes that have already been detected using the special camera. This two-method approach is more accurate than using either one alone. The surgeon will remove the sentinel nodes and they will be examined by a pathologist under a microscope. It will take several days to get the results.
- Wide Local Excision is a procedure in which the melanoma, including the biopsy site as well as an area of normal tissue around it (margins), is removed. It is recommended that lymphatic mapping and the sentinel lymph node biopsy be performed before the wide local excision is done.
After Sentinel Lymph Node Biopsy (SLNB)
The sentinel nodes removed by your surgeon will be examined under a microscope by a dermatopathologist to determine if there is melanoma in the lymph nodes. It has been found that approximately 20% of patients have melanoma in their lymph nodes.