Re-excision Required for Melanoma In Situ with Positive Peripheral Margins
When melanoma in situ has involved peripheral margins, immediate re-excision is mandatory to achieve histologically clear margins and prevent local recurrence. 1, 2
Immediate Management Algorithm
Re-excision Strategy
Perform wide local excision with 0.5-1.0 cm clinical margins measured from the edge of the previous excision scar, as this represents the standard of care for melanoma in situ 1, 2
For lentigo maligna subtype specifically, margins greater than 0.5 cm are frequently necessary due to characteristic subclinical extension that can reach several centimeters beyond visible borders 2, 3
Consider staged excision or Mohs micrographic surgery for head/neck locations, particularly for lentigo maligna, as these techniques provide exhaustive peripheral margin assessment and tissue conservation in cosmetically sensitive areas 1, 2
Critical Pathology Considerations
The central re-excision specimen must undergo permanent section analysis to identify any unsuspected invasive melanoma, which occurs in approximately 12% of melanoma in situ cases 4, 5
If invasive melanoma is discovered on re-excision, wider margins (≥1 cm) become necessary and sentinel lymph node biopsy should be performed before the wide excision 1, 4
Evidence-Based Margin Requirements
Standard Margins Are Often Inadequate
The traditional 5 mm margin clears only 83-86% of melanoma in situ lesions, leaving 14-17% with persistent positive margins 6, 7
A 9 mm margin successfully removes 95-99% of melanoma in situ, representing a significantly superior clearance rate compared to 5-6 mm margins (p<0.001) 2, 7
Head, neck, hands, and feet require wider margins (1.5-2.5 cm) compared to trunk and extremities due to greater subclinical extension in these anatomic locations 6
Lentigo Maligna Requires Special Attention
Lentigo maligna has a 38% incomplete excision rate with standard margins, significantly higher than other melanoma in situ subtypes (p<0.01) 8
Atypical melanocytic hyperplasia extends laterally beyond clinically visible margins, making standard narrow margins unreliable for this subtype 3
Staged contoured excision technique reduces positive margins to 24% by allowing sequential margin assessment before central reconstruction 5
Common Pitfalls and How to Avoid Them
Underestimating Subclinical Extension
Approximately 50% of head and neck melanoma in situ cases require margins >0.5 cm for clearance, so starting with wider margins in these locations prevents multiple re-excisions 1, 2
Lesions >2-3 cm in diameter require wider margins than smaller lesions regardless of anatomic location 6
Missing Invasive Components
Shallow biopsies carry significant risk of underestimating true depth, as focal microinvasion may not be sampled by superficial techniques 4
Even small tumors (<2 cm) harbor unsuspected invasive melanoma in 21% of cases, reinforcing the need for full-thickness central specimen analysis 5
Inadequate Follow-up After Re-excision
Local recurrence of lentigo maligna occurs in 2.9% of completely excised cases, representing persistent disease from inadequate initial margins rather than true metastatic recurrence 8
Recurrence after complete excision of non-lentigo maligna melanoma in situ is only 1.1%, but this still requires long-term surveillance 8
Reconstruction Timing
Delay definitive reconstruction until negative margins are confirmed histologically, as 24% of patients require at least one additional margin re-excision 5
Median time from initial margin excision to final reconstruction is 7 days, allowing for permanent section analysis without prolonged wound management 5
Reconstruction options include local flaps (37%), full-thickness grafts (41%), or split-thickness grafts (20%) depending on defect size and location 5