General
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• Atypical melanocytes in basal layer, individually and in nests (theques), associated with sun damage (eMedicine)

Terminology
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• Also called melanoma arising in Hutchinson’s freckle, actinic melanosis, melanoma on sun damaged skin and solar melanoma
• Note: lentigo maligna (a subtype of melanoma in situ), by definition, does NOT infiltrate into dermis, but lentigo maligna melanoma has at least single cell infiltration into papillary dermis

Clinical features
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• Flat, tan to black with irregular hyperpigmentation, > 2 cm
• 5-15% of (invasive) melanoma; increasing prevalence, particularly among men age 65+ years (J Invest Dermatol 2005;125:685)
• Slow growing lesion of sun exposed skin of elderly whites, often cheek; partial regression is common
• Similar behavior to other melanoma subtypes when depth of invasion is considered, but unusual to die of disease
• Possible origin from progenitor stem cell (strongly CD133+ and CD34+) in outer root sheath of mid-lower hair follicles (Dermatol Ther 2008;21 Suppl 1:S1)

Case reports
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• 51 year old woman with Fitzpatrick skin type III (Dermatology 2008;217:66)
• Collision tumors: 79 year old man with coexisting Merkel cell carcinoma (J Cutan Pathol 2008;35:203), 82 year old woman with coexisting basal cell carcinoma (Am J Dermatopathol 2005;27:319), with coexisting gastrointestinal stromal tumor (Am J Clin Dermatol 2012;13:64)

Treatment
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• Excision with careful margin control (J Am Acad Dermatol 2008;58:142)
• Staged excision for peripheral margin control using permanent sections is required because frozen sections are unreliable (Plast Reconstr Surg 2007;120:1249)
• Possibly radiation (Surg Clin North Am 2003;83:323)
• Possibly imiquimod without (Ann Plast Surg 2008;61:419) or with surgery (Dermatol Surg 2008;34:147)
• Possibly cryotherapy

Dermoscopy
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• Annular-granular pattern (Br J Dermatol 2012;167:280), asymmetric pigmented follicular openings, dark rhomboidal structures and homogeneous areas

Dermoscopy images
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Annular-granular pattern

With slate-gray dots

Typical dermoscopy features

Clinical images
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Various images

Micro description
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• Contiguous growth of atypical melanocytes in basal layer, individually and in nests (theques)
• Cells may be spindled, pleomorphic and have cytoplasmic retraction
• Dermis shows solar elastosis
• Also epidermal atrophy, actinic damage and basilar keratinocyte hyperpigmentation

Micro images
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Atypical melanocytes

     

Various images

Molecular description
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• p.R163Q variant of MC1R gene is associated with lentigo maligna melanoma in mediterranean populations (Br J Dermatol 2013 May 6 [Epub ahead of print])

Differential diagnosis
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• Desmoplastic melanoma: may arise secondary to lentigo maligna
• Lentiginous nevi
• Lentigo maligna in situ melanoma

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