Sentinel lymph node

Why are lymph nodes important in cancer?

Most of the cancers in dogs can spread to lymph nodes, and even tend to do so before spreading to more distant sites such as the lungs or abdominal organs. Looking at the lymph nodes is therefore important to know if the cancer has spread or not, and this assessment is part of the staging of most cancers. 

In human oncology, removing metastatic lymph nodes is a very important part of the treatment of many cancers and recent advances in lymph node dissections have significantly improve the outcome of cancer patients.

How can we know if a cancer has spread to a lymph node?

When a lymph node is enlarged in a cancer patient, it is more likely to be metastatic. Some enlarged lymph nodes are however only “reactive” because of the local inflammation, whilst some apparently normal lymph nodes may contain some cancer cells. Fine-needle aspirates can be performed in a first intent to assess the lymph node. It is relatively cheap, non-invasive and easy to perform. As it only takes a few cells, some small metastases can be missed and removing surgically the entire lymph node provides more reliable information through histological examination. Even then, it may be difficult to reliably identify cancer cells which could be missed. This is an active area of research in which the team at AURA is strongly invested.

In-house cytology of a lymph node with mast cell tumour metastasis

What is sentinel lymph node mapping?

Since the body contains multiple lymph nodes, it is important to identify the one(s) draining the tumour in question. For a long time, lymph nodes were presumed to be draining tumours based on their known location, but several studies have recently shown that it may actually be difficult to predict which lymph node is really draining a tumour. 

Sentinel lymph node mapping is a procedure in which a product is inject around a tumour, before it migrates and accumulate into the first lymph node(s) draining it. These techniques are separated into pre-operative procedures which allow to plan the surgery. A CT scan is generally performed, but we also recently developed an ultrasound technique which allows to decrease costs and avoid general anaesthesia.

Intra-operative techniques may help visualise the lymphatic tracts and lymph nodes to remove, allowing to reduce the time of the surgical procedure, and decreasing the risks of missing a lymph node. Our team at AURA is invested in developing different techniques of preoperative and intraoperative sentinel lymph node mapping. We are convinced that, as in human, improving lymph node management in pets will allow us to treat more efficiently their cancers and increase the chances for long-term remission. 

CT scan sentinel lymph node mapping in a cat with a melanoma on the left ear.