A 52-year-old man presents with a 2 cm dark nodular lesion on his left shoulder with recent onset bleeding and irregular borders. Dermoscopy confirms melanoma with Breslow thickness of 3.2 mm. Which investigation is most appropriate for staging and assessing metastatic disease in this patient?

Explanation

## Investigation Strategy for Melanoma Staging ### Clinical Context This patient has a **thick melanoma** (Breslow thickness 3.2 mm, >2 mm) with high-risk features (nodular morphology, bleeding, irregular borders). Staging investigations must detect regional lymph node involvement and distant metastases. ### Rationale for Sentinel Lymph Node Biopsy (SLNB) **Key Point:** SLNB is the gold standard for staging intermediate-thickness (1–4 mm) and thick (>4 mm) melanomas. It provides the most accurate prognostic information and guides adjuvant therapy decisions. - Detects occult nodal metastases in 15–25% of clinically node-negative patients with thick melanomas - Allows selective lymphadenectomy only if sentinel nodes are positive, avoiding unnecessary morbidity - Provides accurate staging for risk stratification (AJCC 8th edition) ### Staging Imaging After SLNB **High-Yield:** The choice of staging imaging depends on Breslow thickness and SLNB results: | Breslow Thickness | SLNB Status | Recommended Imaging | |---|---|---| | 1–2 mm | Negative | Clinical surveillance; imaging only if symptomatic | | 2–4 mm | Negative | CT chest/abdomen/pelvis ± brain MRI (consider risk factors) | | >4 mm | Negative | CT chest/abdomen/pelvis + brain MRI | | Any | Positive | Staging imaging (CT/MRI) + consideration for PET-CT if high burden | **Clinical Pearl:** PET-CT is **not** routine for stage I–II melanoma (no nodal involvement). It is reserved for stage III (nodal disease) or stage IV (suspected distant metastases) to detect FDG-avid lesions. ### Why This Approach? 1. **SLNB first** → determines nodal status and guides imaging intensity 2. **CT chest/abdomen/pelvis** → detects visceral metastases (lungs, liver, adrenal) 3. **Brain MRI** → detects CNS involvement (10–20% risk in thick melanomas); more sensitive than CT 4. **PET-CT** → reserved for stage III+ or symptomatic patients **Mnemonic:** **SLNB-STAMP** — **S**entinel **L**ymph **N**ode **B**iopsy, then **S**taging **T**omography (CT), **A**dditional **M**RI (brain), **P**ET if nodal/distant disease. ### Why Not the Other Options? - **Option 0 (CXR + ultrasound):** Insufficient sensitivity for occult nodal and visceral metastases; does not address SLNB staging. - **Option 1 (PET-CT + brain MRI):** PET-CT is premature without SLNB confirmation; adds cost and radiation without stage I–II indication. - **Option 3 (Bone scan + LFTs):** Bone scan has low sensitivity for melanoma metastases; LFTs are screening only, not diagnostic imaging.