Sentinel node

The sentinel node is defined as the first node of a lymphatic chain that drains a specific tissue territory, so that, before continuing on its way through the chain, all the lymph coming from said territory It must pass through the sentinel node first.

This concept is of great importance in the field of oncology. In the same way that the lymph from a certain territory must progress in stages through the nodes of a lymphatic chain, the tumor cells that could detach from this same territory, when it is neoplastic, must circulate in stages through the nodes of the chain, being the first of them the sentinel.

Thus, it can be said that the status of the sentinel node, in terms of its invasion or not by neoplastic cells, can translate, with high accuracy, the status of the rest of the chain of the body.

The first case of sentinel lymph node in cancer was reported by Dr. Cabañas in the 1970s when treating cases of penile cancer. Dr. Cabañas is the father of the sentinel node concept in modern surgery in the 90s the technique was popularized with lymphatic mapping in patients with Melanoma by Professor Morton, however, the greater notoriety of the node technique sentinel was developed in breast cancer after Dr. Armand Giuliano in 1998, a student of Dr. Morton developed and began to apply the technique in breast cancer. Since Breast Cancer is extremely frequent in the female population, the sentinel node technique quickly spread throughout the world. In Latin America, the first report was found in Guatemala by Dr. Sergio Ralon at the San Juan de Dios General Hospital in the year 1998 in patients with breast cancer

Uses

This principle is currently applied to the study of two types of neoplasia: breast and melanoma, although it is also being tested experimentally in the colon, stomach, thyroid, and esophagus, as well as in some rare tumors such as stem cell tumors. Merckel.

Target

The basis of this exploration is as follows:

- If the SLN is negative (without tumor invasion), the rest of the chain will also be negative, with the prognostic and therapeutic implications that this entails.

- If the SLN is positive, the rest of the chain may or may not be, but lymphadenectomy of the area and any additional therapeutic actions should be carried out.

currently, after the results of clinical trials, it is determined that it is only necessary to have the SLN result to make the decision for postoperative chemotherapy without the need to perform a complete lymph node dissection, even when neoadjuvant therapy has been used and the lymph nodes were positive for lymph node metastasis

Advantages

The importance of technique is twofold:

- Avoid complete lymphadenectomy of the affected chain. (only in cases in which the SLN is negative for neoplastic cells).

- Carry out a better lymph node staging (second factor of the TNM staging system), since the lymph node with the highest probability of tumor invasion (the Sentinel Node) is studied in depth.

Technique

To carry out the study of the SLN, a tracer must be found that, in some way, simulates the behavior of a malignant cell detached from the main tumor. Several substances have been studied, the most frequently used being the nanocolloid (colloidal sulphide) labeled with 99mTc.

This tracer is administered at the level of the tumor bed, either peritumoral or intratumoral in the case of breast cancer and intradermal in the case of melanoma. Administration is usually done by 4 injections, to try to cover all the possible directions in which a malignant cell could potentially migrate. There is only one exception, which is non-palpable breast cancer. In these cases, as the puncture must be done under ultrasound control, only one dose of the tracer is administered, if possible intratumorally.

To carry out this type of exploration, two pieces of equipment are required: a gamma camera (if possible with a single head because it is easier to maneuver) and an intraoperative gamma probe (in order to be able to locate the activity emitted by the SLN intraoperatively).

In the case of breast cancer surgery, in addition to the radiopharmaceutical (99mTC), a blue dye is used intraoperatively. The radiopharmaceutical is injected before the operation. The blue dye, the most used is Lymphazurin (isosulfan blue) is injected when the patient is already under anesthesia. The blue dye is taken up by the lymphatic channels and allows visual identification of the sentinel node. This makes it easier for the surgeon and more precise, since using both techniques increases the probability of finding the sentinel node. This makes the procedure more effective and precise.

The most widely used dye in North America is isosulfan blue, however, patent blue and methylene blue are also widely used. Each has its advantages and disadvantages. In countries with little access to expensive technology it is common to see reports of the use of methylene blue alone. In Guatemala, Sergio Ralon and Guillermo Puente, heads of Surgery and the Tumor Clinic of the San Juan de Dios Hospital in Guatemala City, report one of the first experiences using only the use of methylene blue for both lymphatic and sentinel node mapping in breast cancer as well as gastric cancer, which reports quite good and acceptable rates of detection of the sentinel node as a predictor of lymph node status in these types of cancer