Sentinel Lymph Node Biopsy

Q. What is the role of sentinel lymph node biopsy in breast cancer and when is it done? Is it done before axillary dissection or to avoid axillary dissection?


What is a sentinel lymph node?


A ‘sentinel’ is defined as a soldier or guard whose job is to stand and keep watch. This might lead somebody to incorrectly believe that a sentinel lymph node somehow guards against the spread of cancer, when it is merely an indicator of spread and a sort of conduit for the malignancy in question to metastasise lymphatically. The concept here is that the route of lymphatic metastasis passes through the sentinel lymph node – so, in theory, if we examine the sentinel lymph node and it does not show signs of metastasis, we can say with a reasonable amount of certainty that the lymph nodes beyond it are not involved, allowing us to not remove the larger group of lymph nodes in question.

Figure 1: This is a helpful diagram to illustrate the position of a sentinel lymph node. For the cancer to spread to the non-sentinel lymph nodes, metastases from the primary tumour must pass through the sentinel lymph node.

Image: M.A. Crane, Lucia & Themelis, George & Tim Buddingh, K & Buddingh, Tim & Harlaar, Niels & Pleijhuis, Rick & Sarantopoulos, Athanasios & G J van der Zee, Ate & Ntziachristos, Vasilis & Dam, Gooitzen. (2010). Multispectral Real-time Fluorescence Imaging for Intraoperative Detection of the Sentinel Lymph Node in Gynecologic Oncology. Journal of visualized experiments : JoVE. 10.3791/2225.

The areas where the concept of a sentinel lymph node is most relevant are breast cancer and malignant melanoma. Since the question is regarding axillary lymph node dissection, I will primarily discuss it in the context of breast cancer. Demonstration of a sentinel lymph node as being negative for tumour cells in a patient of breast cancer can save us the trouble of an axillary dissection and possible future complications like lymphedema.
The process of determining whether the sentinel lymph node contains tumour cells or not is called a ‘sentinel lymph node biopsy’, and this is performed intra-operatively (while the surgery for the removal of the primary tumour is in process) and a ‘frozen section’ of the lymph node is sent for a histopathological evaluation.

How do you identify a sentinel lymph node?

Identification of the sentinel lymph node can be done through a variety of ways. The crudest way is by injection of a blue dye which can be detected visually during the operation.


Figure 2: Blue dye marking the location of the sentinel lymph node in the axilla.
Image: Dr Ben Green, breastendocrinebrisbane.com.au
Other advanced techniques include fluorescence-image guided surgery; and pre-operative lymphoscintigraphy – a technique involving the injection of a dye that can be visualised radiologically. Pre-operative lymphoscintigraphy in conjunction with SPECT (single photon-emission CT) allows for better radiologic visualisation of the lymph node.

What to do with the lymph node once you’ve seen it?

The sentinel lymph node(s) (one or a few primary draining nodes) are removed by an excision biopsy and are typically sent to a pathologist in the form of a ‘frozen section’. The pathologist examines the sample for the presence of tumour cells and informs the surgery team if the sample is positive or negative for tumour cells. If positive, the surgeon goes ahead and removes the axillary group of lymph nodes; but if negative, axillary lymph node dissection is spared.

What are the advantages of preserving axillary lymph nodes at all? Why not just remove them anyway?

Preservation of axillary lymph nodes allows us to better predict the outcomes of breast radiotherapy and avoids its complications on breast reconstruction. It also decreases the risk of lymphedema – swelling of lymphatic vessels that now don’t drain anywhere.

What are the disadvantages of a sentinel lymph node biopsy?

Like other tests, there may occasionally be false negatives, leading to undetected nodal metastasis, which may spread to other parts of the body.

TL;DR

To answer your question in short, a sentinel lymph node biopsy is done intra-operatively to identify if it’s positive for tumour cells or not. If it is, we go ahead and remove the axillary group of lymph nodes. If it isn’t, we let it be.

Hope that cleared it up.

By Dr Anmol Dhawan

References:
  1. M.A. Crane, Lucia & Themelis, George & Tim Buddingh, K & Buddingh, Tim & Harlaar, Niels & Pleijhuis, Rick & Sarantopoulos, Athanasios & G J van der Zee, Ate & Ntziachristos, Vasilis & Dam, Gooitzen. (2010). Multispectral Real-time Fluorescence Imaging for Intraoperative Detection of the Sentinel Lymph Node in Gynecologic Oncology. Journal of visualized experiments : JoVE. 10.3791/2225.
  2. Mannu, G.S.; Navi, A.; Morgan, A.; Mirza, S.M.; Down, S.K.; Farooq, N.; Burger, A.; Hussien, M.I. (2012). "Sentinel lymph node biopsy before mastectomy and immediate breast reconstruction may predict post-mastectomy radiotherapy, reduce delayed complications and improve the choice of reconstruction". International Journal of Surgery.




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