What Is the Sentinel Node?

24 July, 2020
The sentinel node is a very important lymph node in the diagnosis, staging, and treatment of cancers, especially breast cancer. Its correct identification can save the cancer patient from surgeries and other interventions.

Oncological pathologies often lead to the overuse of different procedures when treating patients. The sentinel node technique saves some steps and avoids surgery that would be unnecessary.

The sentinel node is the first node that cancer cells go to when they separate from the primary tumor. It’s not a metastasis in the broad sense of the word, but the mechanism is similar. From localized cancer in an organ, malignant cells move off other areas and some arrive at a nearby lymph node.

For breast cancer, the sentinel node is key in staging, that is, when considering the true extent of the tumor in the body. Through a biopsy of the sentinel node, doctors can predict the evolution of the condition in that person.

In addition, the sentinel node data helps to plan post-biopsy therapy. Based on the cataloged extent of the cancer, doctors can decide whether to use only surgery, chemotherapy plus radiation therapy, or any other combination.

Evolution thanks to the sentinel node

Sentinel lymph node biopsy was an important advance in oncology. Just think that before this technique, a woman with breast cancer used to undergo major surgery where part of the lymphatic chain was removed from her armpit closest to the primary tumor.

This isn’t a minor intervention and one of the most common adverse effects is lymphedema, which consists of obstruction of the lymph circulation. In this case, due to the lack of circulation, the liquid seeps into the soft tissues, inflaming the upper limb.

The removal of the entire lymphatic chain had two objectives: to diagnose the scope of the cancer, and to treat any metastasis already located there. The problem with this technique was that, if the result of the subsequent biopsy was negative, then the entire intervention had been in vain and the woman then had to suffer the adverse effects.

The idea of ​​reducing the size of the surgery is to improve the quality of life of the patients. You will still need intervention, but the incision is smaller and the surgeon will remove the node only if the biopsy reports the presence of malignant cells.

Naked woman raising arm over head.
In breast cancer, the sentinel node is located in the armpit closest to the tumor.

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Sentinel node biopsy

The sentinel lymph node biopsy procedure is part of the protocol for certain breast cancers. Melanomas have been experimented with, but there’s still discussion about their usefulness.

As we mentioned before, this biopsy takes a sample from the first node to which the primary tumor would drain, in order to locate malignant cells. If the result is negative, then we can be sure that the tumor is localized and contained in the organ.

This involves a smaller incision than is required for major lymphatic chain removal surgery, but it can still have side effects. The most common are subsequent bleeding from the wound and puncture site infection. However, the risk is very low.

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How do they know which is the sentinel node?

Woman on examination table getting breast cancer screening.
The best method to find the sentinel node depends on the team of medical professionals.

To perform the biopsy, doctors must first identify the sentinel node. To do this, health teams employ techniques that make this node evident above the others. That way, the surgeon is able to find the correct location for the procedure.

One way to mark the sentinel node is with radioactivity. First, a solution with radiation power is injected in areas near the primary tumor. This solution will migrate to the lymphatic system and radioactivate the first node in the chain.

Another technique is that of using blue dye. Instead of a radioactive substance, the injection carries blue dye, which makes the same journey, passing from the area of the primary tumor to the first nearby node.

The choice of the best method depends on the team treating the condition. Both are efficient in locating the sentinel node and their adverse effects are minimal. The radioactive substance is weak and doesn’t cause internal radiation problems in the cells. On the other hand, the blue dye can generate bluish discoloration of the urine for a time.

What do the biopsy results mean?

There are two ways to proceed after sentinel node biopsy. If the result is negative, this means that they didn’t detect malignant cells, so there’s no need for further surgery. Doctors will assess the patient’s situation and start the corresponding treatment.

In the event of a positive result, surgery should be broadened. This means that cancer cells have been detected in nearby nodes and the tumor has expanded.

As we always warn, early detection is very important in oncology. The earlier the procedure is performed, the sooner the results will be available and the better the prognosis.

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  • Colmenares, Josepmilly Peña, et al. “Detección ganglio centinela con azul patente cáncer de mama localmente avanzado después de quimioterapia neoadyuvante.” Revista Venezolana de Oncología 24.3 (2012): 217-225.
  • Álvarez, Nadia Jesús López, et al. “Biopsia ganglio centinela en cáncer de mama.” RECIMUNDO 3.4 (2019): 279-295.