What is the treatment for in situ melanoma diagnosed with a shallow biopsy?

Management of In Situ Melanoma Diagnosed with Shallow Biopsy

When a dermatologist diagnoses in situ melanoma on a shallow biopsy, you must proceed with wide excision using 0.5-1.0 cm margins, but critically, you should strongly consider performing a narrow-margin re-excision first to ensure accurate staging before definitive wide excision. 1

The Core Problem with Shallow Biopsies

A shallow biopsy of melanoma in situ carries a significant risk of underestimating the true depth of the lesion. 1 The critical issue is that what appears to be melanoma in situ may actually harbor focal microinvasion that was simply not sampled by the superficial technique. 1 This diagnostic uncertainty has major implications:

• Shave biopsies may compromise pathologic diagnosis and complete assessment of Breslow thickness, particularly when the index of suspicion should have been higher. 1
• If microinvasion is present but missed, you may be understaging the patient and potentially missing the window for sentinel lymph node biopsy (SLNB), which should be performed before wide excision. 1
• For lentigo maligna type melanoma in situ specifically, broad shave biopsies extending into deep papillary or superficial reticular dermis are acceptable to optimize sampling, but truly shallow biopsies remain problematic. 1

Recommended Management Algorithm

Step 1: Assess Adequacy of Initial Biopsy

If clinical evaluation suggests the initial biopsy was inadequate for microstaging (i.e., too shallow), perform a narrow-margin excision to obtain deeper tissue before proceeding to wide excision. 1 This is particularly important because:

• You need to definitively rule out invasive melanoma before committing to margins appropriate only for in situ disease. 1
• SLNB must be performed before wide excision and in the same operative setting when indicated. 1
• Once you perform wide excision, lymphatic mapping becomes compromised. 1

Step 2: Definitive Wide Excision Based on Final Pathology

For confirmed melanoma in situ:

• Standard margins: 0.5-1.0 cm measured clinically at the time of surgery. 1
• For lentigo maligna type specifically, surgical margins greater than 0.5 cm may be necessary to achieve histologically negative margins due to subclinical extension. 1
• Depth of excision should extend to (but not including) the fascia. 1

If invasive melanoma is discovered on re-excision:

• Adjust margins based on Breslow thickness:
  • ≤1.0 mm: 1.0 cm margins (Category 1 evidence) 1
  • 1.01-2.0 mm: 1-2 cm margins (Category 1 evidence) 1
  • 2.01-4.0 mm: 2.0 cm margins (Category 1 evidence) 1

  • 4.0 mm: 2.0 cm margins 1

Step 3: Consider Sentinel Lymph Node Biopsy

SLNB should be performed BEFORE wide excision if the tumor is found to be invasive on re-excision. 1 This is why the two-stage approach (narrow re-excision first, then definitive treatment) is so critical when dealing with potentially inadequate initial biopsies.

Special Considerations for Lentigo Maligna

For lentigo maligna melanoma in situ on cosmetically sensitive areas (face, ears, scalp):

• Mohs micrographic surgery or staged excision with permanent sections may be utilized for tissue-sparing excision and exhaustive histologic assessment of peripheral margins. 1
• Permanent section analysis of the central debulking specimen is mandatory to identify potential invasive melanoma, as sampling error can miss microinvasion. 1
• If invasive melanoma is identified intraoperatively during Mohs surgery, the tissue must be submitted for formal pathology review. 1

Critical Pitfalls to Avoid

1. Never perform wide excision with in situ margins if you have any doubt about the adequacy of the initial biopsy. You risk understaging invasive disease and missing the opportunity for SLNB. 1

2. Do not assume a "shallow" biopsy adequately ruled out invasion. The risk of sampling error is substantial, and progression from in situ to invasive disease (or simply missing existing invasion) can occur. 1, 2

3. Avoid planning wide excision margins that will interfere with subsequent lymphatic mapping if deeper pathology reveals invasive disease. 1

4. For lentigo maligna, do not rely on 0.5 cm margins alone – these lesions frequently require wider margins or margin-controlled techniques to achieve histologic clearance due to extensive subclinical spread. 1

Pathology Requirements

Ensure the pathology report from any re-excision includes:

• Breslow thickness in millimeters 1
• Presence or absence of ulceration 1
• Mitotic rate per mm² 1
• Peripheral and deep margin status 1
• Clark level (optional for Breslow >1 mm) 1

The specimen must be read by a pathologist experienced in pigmented lesions. 1