Sentinel Lymph Node Biopsy for Melanoma

Source: Next Steps in Derm

Backed by a mountain of evidence, Dr. Zitelli walked us through the new and changing role of sentinel lymph node biopsy for melanoma in a riveting 20-minute talk presented at the 16th annual ODAC conference. Here are the highlights.

“Let’s separate what’s really evidence based from what you’ve been told.”

Before delving in, Dr. Zitelli skillfully laid the framework for his lecture. The crux of sentinel lymph node biopsy is based on the theory of orderly progression, in which malignant melanoma cells leave the tumor and preferentially enter the lymphatics and the first lymph node. This theory is rivaled by the anatomic pathway, in which malignant melanoma cells may enter the lymphatics or  the blood stream, resulting in simultaneous dissemination.

Which theory is correct?

The overwhelming preponderance of evidence supports the latter anatomic theory – melanoma cells may enter the blood stream directly or the lymphatics, potentially bypassing the sentinel node. This anatomic theory is evidence based. It refutes the theory of orderly progression that the concept of sentinel lymph node biopsy is based on. Another common misconception is that lymph nodes are filters – they are not. Lymph nodes are sampling organs, sampling antigens in order to initiate an immune response.

With the groundwork laid, Dr. Zitelli went on to summarize the emerging evidence for sentinel lymph node biopsy. “This is what you need to know when you counsel a patient in order to obtain true informed consent.”

What you’ve been told: Sentinel lymph node biopsy improves survival
What the evidence shows: There is not a single solid tumor for which sentinel lymph node biopsy has been shown to provide a survival benefit.

We’ve been told that sentinel lymph node biopsy improves survival in intermediate thickness melanoma, because subclinical deposits are removed from the lymph nodes before they can grow. In fact, 33% of patients who underwent sentinel lymph node biopsy, did so because they thought it would improve their survival. Yet, there is not a single solid tumor – melanoma, gastric, renal, thyroid or otherwise – where electively removing normal lymph nodes, even in the case of microscopic involvement, has shown a survival benefit.

A cornerstone trial, the Multicenter Selective Lymphadenectomy Trial (MSLT-1), set out to prove the survival benefit of sentinel lymph node biopsy in melanoma. However, sentinel lymph node biopsy failed to improve melanoma specific survival. Subsequently, MSLT-2 looked at whether removing positive lymph nodes further down the line would improve survival in patients who had positive sentinel lymph nodes – this was also a negative study.

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