What is the recommended treatment for melanoma in situ of the Lentigo maligna type?

Treatment of Melanoma In Situ, Lentigo Maligna Type

For this melanoma in situ (lentigo maligna type) on the malar cheek, perform wide local excision with a minimum 0.5 cm clinical margin, but anticipate that margins greater than 0.5 cm will likely be necessary to achieve histologically negative margins given the characteristic subclinical extension of lentigo maligna. 1, 2

Surgical Excision: The Standard of Care

Surgical excision remains the definitive treatment for lentigo maligna melanoma in situ, as this lesion has no metastatic potential but carries up to a 4.7% lifetime risk of developing an invasive component if left untreated. 1, 3

Margin Requirements for Lentigo Maligna

• Start with 0.5 cm clinical margins as the baseline recommendation for melanoma in situ, but recognize this is often insufficient for lentigo maligna specifically. 1, 2

• Lentigo maligna requires special consideration because atypical junctional melanocytic hyperplasia characteristically extends several centimeters beyond visible margins in an unpredictable pattern—this is the critical pitfall that leads to high recurrence rates. 1, 2

• Approximately 50% of lentigo maligna cases on the head and neck require margins greater than 0.5 cm to achieve histologically clear margins. 2

• Lesions larger than 3.0 cm in diameter typically require margins greater than 1.0 cm for complete excision. 4

Optimal Surgical Approach

Margin-controlled excision techniques are now considered the treatment of choice for lentigo maligna to minimize recurrence while preserving tissue in cosmetically sensitive facial locations. 5

• Modified Mohs micrographic surgery using permanent sections with HMB-45 immunohistochemical staining provides superior margin control and allows for tissue preservation on the face. 4, 5

• Standard wide local excision with 5 mm margins results in unacceptably high recurrence rates and should be avoided. 5

• The goal is complete excision with histologically negative margins—no further treatment is required once clear margins are achieved. 1

Alternative Treatments When Surgery Is Not Feasible

If surgical excision is not feasible due to patient comorbidities, advanced age, or the cosmetically sensitive location on the malar cheek, alternative treatments exist but carry higher recurrence risks:

Topical Imiquimod 5% Cream

• Imiquimod has emerged as a treatment option specifically for lentigo maligna when surgery is contraindicated. 1

• Application regimens typically range from 2-7 times weekly for an average duration of 15.7 weeks (range 7-44 weeks). 6

• Histologic clearance has been demonstrated in multiple case series, though long-term comparative studies are still needed. 1, 6

• Critical caveat: The reason for choosing non-surgical treatment must be clearly documented in the medical record. 1

Radiotherapy

• Radiotherapy can be used selectively for lentigo maligna when surgery is not feasible. 1

• A 5% crude local failure rate has been reported with definitive radiation, with mean time to recurrence of 45.6 months. 1

• Target a margin of at least 10 mm around the visible lesion, as 4 of 5 recurrences occurred at the edge of the radiation field. 1

• Radiotherapy is appropriate for inadequate resection margins when re-excision is not feasible. 1

Combined Immunocryosurgery

• Topical imiquimod combined with cryosurgery represents an alternative option with good therapeutic, functional, and cosmetic results. 7

• This approach has shown disease-free outcomes at 41-48 months follow-up in small case series. 7

Critical Clinical Pitfalls to Avoid

The most common error is underestimating the lateral extent of lentigo maligna, leading to incomplete excision and recurrence rates of 2.9% even after "complete" excision. 3

• Lentigo maligna has significantly higher incomplete excision rates compared to other melanoma in situ subtypes. 3

• The "field effect" of atypical melanocytes extending laterally along the epidermis is not clinically detectable, making visual assessment unreliable. 1

• Recurrence following complete excision occurs almost exclusively in the lentigo maligna subtype, not other melanoma in situ variants. 3

Post-Excision Management

• If margins are histologically clear, no further treatment is required. 1

• If margins are positive after initial excision, re-excision is indicated to achieve clear margins. 1

• Long-term surveillance is warranted given the 2.9% recurrence rate even after complete excision. 3