A 38-year-old woman is found to have a melanoma on her forearm with Breslow thickness of 2.8 mm and no ulceration. There are no clinically palpable lymph nodes. Which investigation is most appropriate to stage this patient and guide treatment decisions?

Explanation

## Staging Investigation for Intermediate-Risk Melanoma ### Risk Stratification and Breslow Thickness **Key Point:** Breslow thickness is the single most important prognostic factor in melanoma and determines the need for sentinel lymph node biopsy (SLNB). ### Breslow Thickness Classification | Breslow Thickness | Stage | Risk of Nodal Metastasis | SLNB Indicated? | |-------------------|-------|--------------------------|----------------| | ≤1.0 mm | IA | <5% | No | | 1.01–2.0 mm | IB | 5–10% | Consider | | 2.01–4.0 mm | IIA–IIB | 10–25% | **Yes** | | >4.0 mm | IIC | >25% | **Yes** | | Any thickness + ulceration | IB–IIC | Increased | **Yes** | **High-Yield:** Breslow thickness 2.8 mm places this patient in stage IIA (intermediate-risk) melanoma, where SLNB is recommended to assess occult nodal disease and guide adjuvant therapy decisions. ### Sentinel Lymph Node Biopsy: Indications & Technique 1. **Indications:** - Breslow thickness 1.0–4.0 mm (intermediate-risk) - Breslow >4.0 mm (high-risk) - Ulceration present - High mitotic rate (≥1/mm²) - Lymphovascular invasion 2. **Technique:** - Intradermal injection of radioactive tracer (technetium-99m) and blue dye near primary tumor - Lymphoscintigraphy to identify sentinel node(s) - Intraoperative gamma probe and visual identification - Histopathological examination (including immunohistochemistry for S-100, Melan-A) 3. **Prognostic value:** - Sentinel node positivity → Stage III (nodal disease) → Adjuvant therapy (nivolumab, pembrolizumab, or interferon-α) - Sentinel node negativity → Stage II → Observation or adjuvant therapy based on other risk factors **Clinical Pearl:** SLNB is both diagnostic (identifies occult nodal disease) and prognostic (upstages 15–20% of clinically node-negative intermediate-risk melanomas), making it essential for treatment planning. ### Why Other Investigations Are Not Appropriate ```mermaid flowchart TD A[Melanoma diagnosed]:::outcome --> B{Breslow thickness?}:::decision B -->|≤1.0 mm| C[Stage I<br/>No SLNB]:::action B -->|1.01-4.0 mm| D[Stage II<br/>Consider/perform SLNB]:::action B -->|>4.0 mm| E[Stage III/IV<br/>SLNB + staging CT]:::action C --> F[Clinical follow-up]:::action D --> G[SLNB for nodal staging]:::action E --> H[SLNB + Imaging<br/>CT/PET-CT]:::action G --> I{SLNB positive?}:::decision I -->|Yes| J[Adjuvant systemic therapy]:::action I -->|No| K[Observation ± adjuvant]:::action ``` **Mnemonic:** **SLNB for Stage II** — Sentinel Lymph Node Biopsy is the staging investigation of choice for intermediate-risk (Breslow 1–4 mm) melanoma.