Melanoma Staging: AJCC / Breslow
Thickness, ulceration, nodal burden, and M-substage that drive melanoma imaging
Quick Answer
Melanoma is staged (AJCC/TNM) chiefly by Breslow thickness and ulceration (T), nodal burden and in-transit/satellite disease (N), and metastatic site with LDH (M). This staging directly shapes nuclear-medicine use: sentinel-lymph-node biopsy stages the early clinically node-negative patient, while FDG-PET/CT is the whole-body tool for stage III–IV disease. Understanding the M-substages (M1a–M1d) clarifies why melanoma imaging emphasizes unusual sites and a separate brain MRI.
Primary Tumor (T) — Thickness & Ulceration
Breslow thickness (depth in mm) and ulceration are the dominant primary-tumor prognostic factors (mitotic rate is recorded but no longer sub-stages T1 in the 8th edition):
| T | Breslow thickness | a / b |
|---|---|---|
| T1 | ≤ 1.0 mm | a (< 0.8 mm, no ulceration) / b (0.8–1.0 mm, or ulcerated) |
| T2 | > 1.0–2.0 mm | a (no ulceration) / b (ulceration) |
| T3 | > 2.0–4.0 mm | a / b (by ulceration) |
| T4 | > 4.0 mm | a / b (by ulceration) |
Thicker and ulcerated tumors carry higher metastatic risk — and lower the threshold for sentinel-node biopsy.
Regional Disease (N) — Nodes & Non-Nodal Regional Spread
N integrates the number of involved nodes and whether disease is clinically occult (microscopic, sentinel-detected) vs clinically detected (macroscopic), plus non-nodal regional disease — microsatellites, satellites, and in-transit metastases. Any of these defines stage III. This is why lymphoscintigraphy/sentinel-node mapping is central to early nodal staging (FDG-PET misses microscopic nodal disease).
Distant Metastasis (M) — Site + LDH
M-substage combines anatomic site with a serum LDH modifier (0 = normal, 1 = elevated):
| M | Site |
|---|---|
| M1a | Distant skin/soft tissue/nodal |
| M1b | Lung |
| M1c | Other non-CNS visceral |
| M1d | CNS (brain) |
Elevated LDH worsens each substage. M1d (CNS) is prognostically important and drives the brain-MRI requirement — FDG-PET is insensitive for brain metastases (high cortical uptake).
Stage Groups (Overview)
- Localized: stage I–II (by T/ulceration).
- Regional: stage III (nodal, satellite, in-transit).
- Distant: stage IV (any M).
How Staging Drives Imaging
- Early, thin, cN0 (stage I–II): sentinel-lymph-node biopsy (lymphoscintigraphy ± SPECT/CT) — PET has low yield for micrometastases.
- Stage III–IV: FDG-PET/CT for whole-body staging, surgical planning, and detecting distant/unusual metastases; brain MRI separately.
- Response: FDG-PET tracks immunotherapy/targeted-therapy response — with the irAE/pseudoprogression caveats (see the melanoma page).
Common Pitfalls
- Using FDG-PET to "clear" the nodes in early, cN0 melanoma — it misses micrometastatic disease (use sentinel-node biopsy).
- Forgetting the brain-MRI requirement for stage III–IV (PET brain insensitivity).
- Overlooking in-transit/satellite disease that defines stage III.
- Ignoring the LDH modifier in M-substaging.
Board Pearls
Melanoma T-stage is driven by Breslow thickness and ulceration; N by nodal burden and in-transit/satellite disease (any = stage III); M by site + LDH (M1a soft-tissue/nodal, M1b lung, M1c non-CNS visceral, M1d CNS). This maps directly onto imaging: sentinel node stages the early cN0 axilla/basin; FDG-PET/CT stages III–IV.
FDG-PET must not be used to clear the nodes in early, clinically node-negative melanoma — it misses micrometastases; sentinel-lymph-node biopsy (lymphoscintigraphy) is the stager.
M1d (CNS) and the brain-MRI requirement follow from PET's insensitivity for brain metastases, and melanoma's propensity for unusual metastatic sites (bowel, subcutaneous, myocardium, spleen) is why whole-body stage-III–IV FDG-PET is reviewed deliberately. Elevated LDH worsens every M-substage.
Related Pages
- Disease: Melanoma (imaging by stage, immunotherapy response, irAEs).
- Related studies: Lymphoscintigraphy & sentinel node (early nodal mapping).
- Tracer: FDG.
Figure / Diagram Suggestions
- A T-stage ladder (Breslow thickness × ulceration).
- An M1a–M1d site map with the LDH modifier.
- A stage-based imaging decision (sentinel node early vs FDG-PET III–IV + brain MRI).
Self-Check (Board-Style)
Q1. A 0.7-mm non-ulcerated melanoma with clinically negative nodes — how are the nodes best staged?
Answer: By sentinel-lymph-node biopsy (lymphoscintigraphy) if indicated — FDG-PET misses micrometastatic nodal disease in early, cN0 melanoma.
Q2. What two primary-tumor features dominate T-staging in the AJCC 8th edition?
Answer: Breslow thickness and ulceration (mitotic rate is recorded but no longer sub-stages T1).
Q3. A patient has brain metastases. What M-substage is this, and why is MRI required rather than PET?
Answer: M1d (CNS). Brain MRI is required because high physiologic cortical FDG makes PET insensitive for cerebral metastases.
Q4. What non-nodal regional findings define stage III melanoma?
Answer: Microsatellite, satellite, and in-transit metastases (along with nodal involvement) define stage III.
Evidence & sources
https://nuc.med/melanoma-staging-ajcc/ Report an issue