May be difficult to identify, especially if desmoplastic type or heavily inflamed
Papular Growth in Pigmented Patch The marked area , prior to biopsy, shows a papular growth in an ill-defined pigmented patch. This raises concern for a microinvasive melanoma. (Courtesy J. Finch, MD.)
Darkly Pigmented Papule on Elderly Earlobe The marked lesion is concerning for melanoma . This lesion stands out among the many seborrheic keratoses on the left face and neck. (Courtesy J. Finch, MD.)
Atypical Pigmented Lesion With Inflammatory Regression of LMM This broad, atypical melanocytic proliferation displays fibrosis and patchy, inflammatory infiltrate , consistent with inflammatory regression. Even the solar elastosis is interrupted in the area of fibrosis.
Microinvasive Nest of LMM Above the lentiginous atypical, melanocytic proliferation , there is a prominent invasive nest in the papillary dermis. Note the fibrosis (interrupted solar elastosis) and inflammation .
TERMINOLOGY
Abbreviations
• Lentigo maligna melanoma (LMM)
Synonyms
• Invasive melanoma, lentigo maligna type
• Hutchinson freckle (clinical term, which typically refers to melanoma in situ, lentigo maligna type)
Definitions
• Indolent melanoma subtype that evolves slowly and usually presents on head and neck (sun-exposed regions) in older patients
CLINICAL ISSUES
Epidemiology
• Age
Older patients, typically > 60 years old
Site
• Usually on head and neck (sun-exposed regions)
Presentation
• Broad patch with nodule, may grow 5-10 cm or larger
• Variegated colors
• Irregular borders
Natural History
• Slowly evolving, indolent but invasive type melanoma
Treatment
• Surgical approaches
Complete excision; margins depend on depth of invasion
Mohs surgery if poorly defined margins; recurrence rates of < 1%
• Drugs
Imiquimod cream is controversial but has shown promise for subset of patients
– Long-term follow-up and several posttreatment biopsies are encouraged, even with lack of clinical recurrence
Prognosis
• Surgical margins of at least 5 mm give cure rates of 90-95%
MICROSCOPIC
Histologic Features
• Severely atypical compound melanocytic proliferation with junctional lentiginous component (typical of lentigo maligna)
Confluence of melanocytes replacing basilar keratinocytes, often forming cleft
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