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Nuclear Conventional Medicine

The Sentinel Lymph Node in Oncology (first part)

Introduction

First of all, it is important to know that cancer may spread in the whole body (to metastasize, i.e. to send – in the whole body – malignant cells that will develop in other organs) in two ways; either malignant cells seep into the blood vessels which supply the tumour itself (hematogen dissemination), or they seep into lymphatic vessels which originate from all the tissues (lymphogenic dissemination) and from there can seep into the blood and the other organs. In this second way, the malignant cells will meet with lymp nodes – structures that will act as filters and in which the malignant cells will develop and – after – metastasize to others organs. The prognosis depends largely on the invasion of the nodes. Actually, the surgical approach to numerous cancers has for a long time consisted – and it is still the case – in a resection of the tumour itself and of the lymph nodes from the nodal groups that drain the tumour and that may be affected.

 

Nevertheless, the nodal invasion varies (from 5 to 60% of risk to find positive nodes according to the size) and is also difficult to predict (to palpate an axillary node does not mean that it is invaded, and don’t do it does not mean that some nodes won’t be invaded). Therefore, nodes can be removed ‘to no purpose’ because they are not affected by the disease – this is the case in 80% of small mammary tumours). Yet some complications go with these nodes resections; in breast cancers, the best known is the ‘big arm’.

 

Just like the therapeutic intervention will now be as minimal as possible (in breast cancers, we went from a resection of the whole mammary gland to resections limited to the tumoral lesion of the breast), the surgical approach to nodal chains is now also more and more targeted.

 

Here comes the concept of ‘sentinel lymph node’.

According to this principle:

• if a tumour metastasizes by lymphatic way, it is by one or more particular lymph vessels that lead to one or more specific nodes (in nodal chains that can count up to 40 nodes), and
• if these ‘sentinel lymph nodes’ selectively resected are not affected by the disease (if no cancer cell is found inside them), there is no risk for the others to be affected and therefore they don’t have to be removed.
• on the other hand, if they are affected, it can also be the case for the others and then – secondly – the nodes of the same group have to be removed, or another treatment has to be considered.

This selective approach to the sentinel lymph nodes that determines the ensuing surgical act on others ganglionic structures was first applied to melanomas and then to mammary tumours. Nowadays, almost every cancer has been studied trough this technique, which is more and more used : Merkel cancer, vulva cancer, uterus cancer, head and neck cancer, prostate cancer,…

 

One ? No, some sentinel lymph nodes…

We can speak of ‘sentinel lymph node’ in the singular as a concept, but in reality there are more than only one, and sometimes located in different areas of the body !

Second part of the document (In practice…): click here

 

Person in charge : Pr Patrick Flamen