Skin Cancer Resection Margins
Basal Cell Carcinoma (BCC)
For low-risk, well-defined primary BCCs less than 2 cm in diameter, excise with 4-mm clinical margins of normal-appearing skin. 1
Low-Risk BCC Margins
- 4-mm margins are appropriate for clinically well-defined, low-risk tumors less than 2 cm in diameter and are expected to achieve complete removal in 95% of cases 1
- Excision should extend to mid-subcutaneous adipose tissue with histologic margin assessment 1
- Any peripheral rim of erythema around the BCC must be included in the presumed tumor border 1
High-Risk BCC Margins
- 6-mm or wider margins are necessary for high-risk features including: 1, 2
- Tumors ≥2 cm in size
- Poorly defined clinical borders
- High-risk anatomic locations (ear, lip, scalp, eyelids, nose)
- Aggressive histologic subtypes (morpheaform, infiltrative, micronodular)
- Recurrent tumors
Alternative Approaches
- Mohs micrographic surgery is recommended for high-risk BCCs, recurrent lesions, or when tissue preservation is critical in anatomically constrained sites 3, 4
- Narrow 2-3 mm margins may be considered for well-defined facial BCCs in cosmetically sensitive areas, but carry a 13-24% risk of positive margins requiring re-excision 5
Critical Pitfall: Facial BCCs excised with 1-3 mm margins have unacceptably high positive margin rates (13-24%), making standard 4-mm margins or Mohs surgery preferable to avoid repeat procedures 5
Cutaneous Squamous Cell Carcinoma (SCC)
For low-risk, well-defined primary SCCs, excise with 4-mm clinical margins; for high-risk SCCs, use 6-mm or wider margins. 1, 2
Low-Risk SCC Margins
- 4-mm margins are adequate for most primary SCCs with low-risk features 1, 2
- The NCCN guidelines recommend 4-6 mm clinical margins for standard excision of low-risk SCC 1
- Excision should extend to mid-subcutaneous adipose tissue 1
High-Risk SCC Margins
- Minimum 6-mm margins are recommended for tumors with any of these features: 2
- Size ≥2 cm in diameter
- Histologic grade 2 or higher (poorly differentiated)
- Invasion into subcutaneous tissue
- High-risk anatomic locations (ear, lip, scalp, eyelids, genitalia)
- Perineural invasion
- Immunosuppressed patients
Large Tumors
- For SCCs >20 mm in area without other high-risk factors that can be repaired primarily, 10-mm clinical margins may be used 4
Alternative Approaches
- Mohs micrographic surgery or resection with complete circumferential peripheral and deep margin assessment is recommended for high-risk SCCs 4
Critical Pitfall: Underestimating clinical tumor borders is common—any erythema surrounding the visible SCC must be considered part of the tumor when planning margins 1
Melanoma
For invasive melanoma ≤2 mm Breslow thickness, excise with 1-cm margins; for melanoma >2 mm thickness, excise with 2-cm margins. 6
Melanoma In Situ (MIS)
- 0.5-1.0 cm margins are recommended for melanoma in situ 6
- Lentigo maligna type MIS may require wider margins or Mohs surgery due to extensive subclinical extension, particularly on the head and neck 6, 7
- Mohs micrographic surgery or staged excision with permanent sections may be utilized for MIS on the face, ears, or scalp for tissue-sparing excision 6
T1 Melanoma (≤1.0 mm Breslow thickness)
- 1-cm margins are recommended based on Level I/II evidence from randomized controlled trials 6
- This applies to melanomas on the trunk and extremities 6
T2 Melanoma (>1.0 to 2.0 mm Breslow thickness)
- 1-2 cm margins are recommended, with the specific margin determined by anatomic location and functional/cosmetic considerations 6
- The American Academy of Dermatology guidelines support both 1-cm and 2-cm margins for this category based on randomized trials 6
- A minimum 2-cm margin is preferred when feasible to minimize locoregional recurrence risk 6
T3 Melanoma (>2.0 to 4.0 mm Breslow thickness)
- 2-cm margins are recommended 6
- The Intergroup Melanoma Trial showed no difference in local recurrence or survival between 2-cm and 4-cm margins 6
T4 Melanoma (>4.0 mm Breslow thickness)
- 2-3 cm margins are recommended, with 3-cm margins preferred when anatomically feasible 6
- One randomized trial comparing 1-cm versus 3-cm margins showed significantly increased locoregional recurrence with 1-cm margins 6
Depth of Excision
- Excision should extend to (but not including) the fascia 6
Special Anatomic Considerations
Head, Neck, and Acral Sites
- Narrower margins may be necessary to preserve function and cosmesis at anatomically constrained sites 6, 8
- However, sub-1 cm margins for invasive melanomas at acral or head/neck sites are generally not recommended until further studies are available 6, 8
- Most prospective randomized trials excluded head, neck, and acral melanomas, limiting evidence for these sites 6
Acral Melanoma Specific Guidance
- For acral melanoma in situ: 0.5-1.0 cm margins 8
- For invasive acral melanoma ≤2 mm: 1 cm margins 8
- For invasive acral melanoma >2 mm: 2 cm margins 8
- Functional preservation is critical, but margins should not be compromised below 1 cm for invasive disease 8
Sentinel Lymph Node Biopsy (SLNB)
- SLNB should be performed before or concomitant with wide excision whenever possible 6
- SLNB is indicated for: 6
- T1b melanoma (≤1.0 mm with ulceration or 0.8-1.0 mm with or without ulceration)
- All melanomas >1 mm thickness (≥T2a)
- SLNB is not indicated for melanoma in situ or T1a melanoma unless other adverse features are present 6
Critical Pitfalls:
- Never use sub-1 cm margins for invasive melanoma except in highly selected cases at anatomically constrained sites after multidisciplinary discussion 6, 8
- Failing to perform SLNB before wide excision complicates lymphatic mapping and may compromise staging 6
- Inadequate initial biopsy depth (shave biopsies) can underestimate Breslow thickness and lead to inappropriate margin selection 7
- For lentigo maligna melanoma, permanent section analysis of the central debulking specimen is mandatory to identify occult invasive melanoma that would require wider margins 7