The sentinel node (also known as guard node) is the first lymph node that filters the tumor’s fluid.
The sentinel lymph node biopsy (SLNB) uses a method that consists of injecting a special dye or a radioactive colloid in the breast in order to identify the sentinel node. The sentinel node is then removed for further anatomopathological examination.
During a breast cancer treatment, the sentinel node biopsy helps to:
- avoid axillary node dissection (AND) if the cancer hasn’t spread to the armpit area (axillae). This may concern up to 70% of the patients who have a tumor measuring less than 3 cm.
- focus the hystopathological analysis on a small number of lymph nodes. (French National Authority for Health, 2002 report)
Therefore, this method consists of removing the first lymph node of the armpit assuming that if this lymph node is negative, the rest of the nodes will be negative too, so it’s unnecessary to remove them. Overwhelmingly this hypothesis has appeared to be true.
How to identify the sentinel lymph node (guard node)?
On the eve prior to surgery, the surgeon injects a low-level radioactive isotopic material into the breast. This material gradually moves towards the first lymph node: the sentinel node.
Within a few hours, an “x-ray” (Lymphoscintigraphy) identifies the sentinel node.
In the morning (or in the afternoon, if the injection took place in the morning), at the start of the surgery (in most cases under general anesthesia), the surgeon injects a blue dye into the breast as a second marker.
The surgeon uses a small probe to detect the area where the isotope has been absorbed. The surgery begins by making an incision into this area.
The surgeon removes the nodes that have been affected either by the blue dye, by the isotope or by both. In fact it is not uncommon that the sentinel node biopsy affects 2 or 3 lymph nodes.
The sentinel lymph node(s) are then sent to an anatomopathologist specialist who will:
- immediately examine the nodes under the microscope (extemporaneous examination): if the results of this first examination are negative, the surgical procedure ends here, as the probability that other lymph nodes have been affected is very low. This spares a complete lymph node dissection,
- perform a close and full analysis in a laboratory. The results are returned in 7 days. If cancerous cells are present, the treatment should be completed by an axillary node dissection.
When to practice the sentinel lymph node method?
It is not possible to proceed to a sentinel lymph node biopsy (SLNB):
- when the doctor finds a suspect lymph node in the armpit area or when the radiologist has identified a lymph node with a tissue withdrawal,
- when the tumor is too large or multifocal (in this case there is a bigger risk for the armpit to be affected and therefore the benefit of a sentinel lymph node biopsy is lower),
- when the patient has already had a lumpectomy or surgical biopsy. The sentinel lymph node may well be concealed if previous surgery has disconnected the lymph vessels. That’s why it is recommended to perform micro biopsies to diagnose cancer and suggest a sentinel lymph node biopsy before the main surgery,
- When the patient has had previous breast surgery (breast reduction, axillary incision for inserting an implant), radiotherapy or chemotherapy.
In all these cases it is preferable to perform a classic axillary node dissection.
It is possible to perform a sentinel lymph node biopsy in the following cases:
- invasive breast cancer confirmed by a micro or micro preoperative biopsy,
- a unifocal cancer measuring less than 3 cm,
- extended in situ carcinoma,
however, this method is not advisable during a preoperative treatment (surgery, chemotherapy, hormone therapy or radiotherapy).