Sentinel Node Biopsy in Melanoma

The role of sentinel node biopsy in melanoma is an ongoing discussion. Recent revisions to the AJCC Criteria have shifted the landscape. This article explores melanoma guidelines and recent revisions.

In this Article on Sentinel Node Biopsy

5 Key Points

Definition of Sentinel Node Biopsy

The definition of "sentinel lymph node" has evolved since Morton et al’s initial publication on the role of lymphoscintigraphy for melanoma in 1992^{​​1​​}.

Role of Sentinel Node Biopsy in Melanoma

Prognosis

Sentinel Node Biopsy (SLNBx) provides prognostic data on all depths of melanoma^​2. For example, a patient with pT1b melanoma has 2 options:

• No SLNBx: melanoma is now classified as a clinical Stage 1B with 5-year and 10-year survival of 97% and 93%, respectively^​3.
• SLNBx: melanoma is now classified as a pathological Stage 1A with a 5-year and 10-year survival of 99% and 96%, respectively^​3.

These prognostic implications are also relevant to thin melanomas (BT<1mm)^​4,5​

Treatment Pathways

The primary role of sentinel node biopsy is changing from that of a prognostic indicator to one that now influences access to adjuvant therapy^​6​.

For those with a positive sentinel node, upstaging the disease allows earlier identification for adjuvant therapies. It also allows them to be categorized in a “high-risk follow-up group”^​7​.

Performing Sentinel Node Biopsy in Melanoma

Indications

There are two main indications for sentinel node biopsy in melanoma.

• Primary Cutaneous Melanoma ≥ pT2a
• Primary Cutaneous Melanoma ≥ pT1b should be considered, especially if Lymphovascular Invasion or Mitotic rate ≥ 2/mm

The mitotic rate has been removed in version 8 of the AJCC guidelines. An increase in mitotic rate decreases melanoma-specific survival^​3.

It is not currently indicated for T1a melanomas. The rationale for this cutoff is based on findings demonstrating that the frequency of sentinel lymph node metastasis is <5% (Swetter, 2019)

Risk of Positive Sentinel Node

The risk of finding a positive sentinel node is correlated to the stage of the depth of the disease, as described below:

• pT1a: <10% ^8,9
• pT1b: 5-12% ⁶
• BT > 4mm: 30% ^8,10

Techniques

The 3 commonly used techniques for sentinel node biopsies are radioactive isotope, blue dye or indocyanine green. Here is an overview of their key points:

Radioactive Isotope

• The current standard method of lymphatic mapping
• Intradermal injection of a radiotracer at the tumour site & lymphoscintigraphy
• Handheld gamma probe or a camera is used intraoperatively to guide dissection and detect the appropriate sentinel node(s).
• Technetium-99m–labelled radiocolloids are the most commonly used radiotracers for lymphatic mapping

Blue Dyes

• Blue dyes were initially used by Morton et al.
• Blue dye alone has shown to have a sensitivity of 81% (Silvestri, 2019).
• Patent Blue V, isosulfan blue and methylene blue are commonly used.
• Rare risks include anaphylactic reactions, obscured intraoperative dissection, tattooing, and interference with pulse oximetry

Indocyanine Green

• Indocyanine green is a fluorescent tricarbocyanine dye
• The sensitivity of sentinel lymph node biopsy is reported as 91- 98%, a specificity of 100% (Clloyd, 2014).
• It cannot be used in patients with iodine or shellfish allergies.

Timing of Sentinel Node Biopsy

The standard of care is to provide a sentinel lymph node biopsy at the time of wide local excision. Studies have found that sentinel lymph node biopsy after wide local excision is feasible with no difference in recurrence or survival with a delayed sentinel lymph node biopsy^16-21.

Positive Sentinel Node Biopsy in Melanoma

Completion Lymph Node Dissection in Melanoma

Complete lymph node dissection should not be routinely recommended for patients who have a positive sentinel node biopsy^​6​. Consider this treatment option in patients who are high risk of regional relapse based on their sentinel node results:

• Extra-capsular spread
• 3 or more sentinel nodes
• Dewar Criteria^​12​ (multifocal and extensive).
• Node-only recurrence having failed first-line systemic treatment.

The MSLT-2^​13​ and DeCOG^​14​ Trials reported on the outcome of patients with a positive sentinel node randomised into observation and surgery. Key results include:

• No survival advantage of completion lymph node dissection over radiological observation
• Increase risk of nodal recurrence in those patients with observation

Patients undergoing immediate lymph node dissection have

• Increased rate of regional disease control^​13​
• Prognostic information^​13​
• No increase in melanoma-specific survival^​13​
• An increased risk of morbidity in nodal dissection patients^​15​

With head and neck melanomas, adjuvant therapy is preferred to neck dissection^​3​.

Adjuvant Therapy in Melanoma

Discussed in more detail: Oncological Adjuvant Therapies in Melanoma

Current guidelines state adjuvant therapy should be available to Stage 3 patients.

Generally speaking, patients deemed at high risk with a positive sentinel node should be considered for melanoma adjuvant therapy. A lymph node dissection could be considered if they have a node-only recurrence post-adjuvant treatment.

Radiological Observation in Melanoma

There is currently no consensus for ideal imaging in melanoma^​7​

Current options include:

• Ultrasound: MLST and DeCOG Trials but does have operator dependability^​5​
• CT/PET: more sensitive to picking up recurrences^​5​
• MRI is used in some UK centres^​6​

Imaging surveillance will differ for those on adjuvant systemic therapy.

AJCC Version 8 Updates

This article is written with the most recent version of AJCC and other publications, as referenced below. The following is a list of V8 updates^​3​

• Tumor thickness: record to the nearest 0.1 mm, not 0.01 mm
• New pT1a <0.8 mm without ulceration
• New pT1b 0.8‐1.0 mm with or without ulceration or <0.8 mm with ulceration
• Mitotic rate no longer a T category criterion
• Pathological (but not clinical) stage IA is revised to include T1b N0 M0 (formerly pathologic stage IB);
• The N category descriptors “microscopic” and “macroscopic” for regional node metastasis are redefined as “clinically occult” and “clinically apparent and subcategories are revised, with the presence of microsatellites, satellites, or in‐transit metastases now categorized as N1c, N2c, or N3c based on the number of tumor‐involved regional lymph node
• Descriptors are added to each M1 subcategory designation for lactate dehydrogenase (LDH) level (LDH elevation no longer upstages to M1c)
• A new M1d designation is added for central nervous system metastases.

References

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