What is the recommended treatment for in situ melanoma?

Treatment of In Situ Melanoma

For in situ melanoma, surgical excision with a 0.5 cm (5 mm) margin around the visible lesion is the standard of care, though larger margins may be necessary for lentigo maligna melanoma to achieve histologically negative margins. 1

Primary Treatment Approach

Standard Surgical Margins

• Excise with a measured 0.5 cm margin around the visible lesion for typical in situ melanoma 1
• This recommendation is based on NCCN panel consensus in the absence of prospective clinical trials 1
• The clinical/surgical margins refer to those taken at surgery and do not necessarily correlate with gross pathologic/histologic margins 1

Special Considerations for Lentigo Maligna

Lentigo maligna and in situ melanoma present unique challenges due to characteristic, unpredictable subclinical extension of atypical junctional melanocytic hyperplasia, which may extend several centimeters beyond visible margins 1

• For large in situ lentigo maligna melanoma, surgical margins greater than 0.5 cm may be necessary to achieve histologically negative margins 1
• Various approaches to achieve complete surgical excision with meticulous margin control have shown high local control rates at some institutions, though not universally accepted 1

Anatomic Modifications

• Surgical margins may be modified to accommodate individual anatomic or cosmetic considerations 1
• Modifications may be needed for preservation of function in melanomas of the fingers, toes, face, and ear 1

Alternative Treatment Options

When Surgery Is Not Feasible

Although surgical excision remains the standard of care, alternatives exist when surgery is not feasible due to comorbidity or cosmetically sensitive tumor location 1

Topical Imiquimod

• Has emerged as a treatment option, especially for lentigo maligna 1
• However, long-term comparative studies are still needed 1
• NCCN guidelines do not include specific recommendations for this treatment option 1

Radiotherapy

• Has been used selectively for lentigo maligna 1
• A retrospective review showed a 5% crude local failure rate with definitive radiation, with mean time to recurrence of 45.6 months 1
• Four of five recurrences occurred at the edge of the radiation field, suggesting targeting a margin of at least 10 mm around the visible lesion 1
• Should be considered for inadequate resection margins when re-excision is not feasible, such as in head and neck melanoma 1

Important Clinical Pitfalls

Inadequate Margins

The commonly recommended 5 mm margin may be inadequate in certain situations. Research data suggests that only 83-86% of melanoma in situ are successfully excised with a 6 mm margin 2, 3. While guidelines recommend 0.5 cm margins based on consensus, studies show 9 mm margins remove 98.9% of melanoma in situ 2. This discrepancy highlights the tension between guideline recommendations and research findings.

Lentigo Maligna Specific Issues

• Lentigo maligna has higher incomplete excision rates compared to other melanoma in situ subtypes 4
• Recurrence following complete excision of lentigo maligna is 2.9%, higher than non-lentigo maligna subtypes 4
• Lesions on the head and neck or those with diameter greater than 1 cm may require wider margins 3

No Role for Sentinel Lymph Node Biopsy

• SLNB is not indicated for in situ melanoma as it is a minimally invasive staging procedure for identifying subclinical nodal metastases, which do not occur with in situ disease 1