Breslow's Intermediate Thickness in Melanoma
Breslow's intermediate thickness melanoma is defined as melanoma measuring >1.0 to 4.0 mm in depth, corresponding to T2 or T3 stage in the AJCC staging system. 1, 2, 1
Definition and Clinical Significance
Intermediate-thickness melanomas represent a critical category in melanoma staging where:
- Lower boundary: >1.0 mm Breslow thickness
- Upper boundary: ≤4.0 mm Breslow thickness
- AJCC staging: Classified as T2 (>1.0-2.0 mm) or T3 (>2.0-4.0 mm)
The definition has remained consistent across multiple ASCO/SSO guideline iterations from 2012 through 2018, reflecting its clinical utility and reproducibility 1, 2, 1.
Why This Category Matters
Sentinel lymph node biopsy (SLNB) is routinely recommended for all patients with intermediate-thickness melanoma because this population has:
- Sufficient risk of nodal metastases to justify the procedure (higher than thin melanomas)
- Better regional disease control potential compared to observation alone
- Improved disease-free survival when nodal disease is detected early 2
The 10-year follow-up data from MSLT-I demonstrated significantly better disease-free survival in the SLNB group versus observation for intermediate-thickness melanomas (HR 0.76, P=0.01), though melanoma-specific survival differences were not statistically significant 2.
Risk Stratification Within Intermediate Category
Within intermediate-thickness melanomas, specific factors predict higher sentinel node positivity rates 2:
- Younger age (<60 years)
- Greater thickness (1.50-4.00 mm vs 1.00-1.49 mm)
- Lack of tumor-infiltrating lymphocytes
- Lymphovascular invasion
- Microsatellitosis
Contrast with Other Categories
To clarify the boundaries:
- Thin melanomas: ≤1.0 mm (T1) - SLNB not routinely recommended except for high-risk T1b lesions 2
- Thick melanomas: >4.0 mm (T4) - SLNB may be offered primarily for staging purposes 2
The intermediate category represents the "sweet spot" where SLNB provides the most clear-cut benefit for staging and regional disease control, with moderate evidence quality and strong recommendation strength 2.