Lentigo Maligna

Lentigo maligna is melanoma in situ, a precancerous lesion that may progress to an invasive melanoma (specifically lentigo maligna melanoma subtype). This condition typically occurs in sun-damaged areas (e.g., face and neck) of elderly patients. Lentigo maligna presents as a brown macule with color variegation and asymmetrical borders that grow slowly. The lesion should be biopsied to confirm a diagnosis and surgical excision with a safety margin is the 1st-line treatment.

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Overview

Definition

Lentigo maligna (also known as Hutchinson melanotic freckle) is melanoma in situ. This type of precancerous lesion may progress to lentigo maligna melanoma.

Epidemiology

  • Peak incidence between 65 and 80 years of age
  • Precursor to the 3rd most common melanoma subtype (lentigo maligna melanoma)
  • Women > men
  • Incidence is 13.7 per 100,000.

Etiology

  • Genetic mutations:
    • Compared with other melanoma subtypes, there is an increased likelihood of KIT mutations.
    • Other mutations include CCND1, MITF, NRAS, and p53.
  • Risk factors:
    • Cumulative (over time) ultraviolet radiation
    • Genetic conditions:
      • Oculocutaneous albinism
      • Xeroderma pigmentosum
      • Porphyria cutanea tarda
    • X-ray irradiation
    • Use of estrogen/progesterone 
    • Use of non-permanent hair dye

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Clinical Presentation

  • Majority occur on the head/neck (mainly the cheek).
  • Variable color: 
    • Light brown to black (may have color variegation)
    • May have pink/white areas indicating inflammation or regression
  • Asymmetric
  • Poorly defined borders
  • Smooth (nonpalpable)
  • Slow growth → speckles (as melanoma enlarges)
  • Indicators of possible progression to invasive melanoma:
    • Raised/palpable areas
    • Sharp borders
    • Darker pigmentation
  • Surrounding skin usually manifests solar skin damage:
    • Actinic keratoses
    • Solar elastosis
    • Solar lentigines

Lentigo maligna: an asymmetric brown macule with color variegation present on the left cheek

Image: “Lentigo maligna” by kilbad. License: CC BY 3.0

Diagnosis

History

  • Amount of sun exposure
  • Other skin cancers
  • Family history of melanoma
  • Hereditary diseases

Physical exam

  • Complete/thorough skin exam should be performed.
  • Synchronous malignant and premalignant lesions are not uncommon in individuals with extensive sun damage to the skin.

Dermoscopy

  • Asymmetric pigmented follicular openings (pseudonetwork)
  • Progression of findings:
    • Early stage: peppering of pigmentation around follicular ostia (blue-gray dots)
    • Coalescence of blue-gray dots into polygonal lines and rhomboidal structures
    • Late stage: homogeneous dark-brown to black blotches blocking the follicular ostia

Reflectance confocal microscopy

  • Availability of this technique is limited.
  • Requires specialized training
  • More sensitive, but less specific for lentigo maligna diagnosis than dermoscopy

Histology

  • Gold standard for lentigo maligna diagnosis
  • Sample obtained via:
    • Excisional biopsy (ideal)
    • Punch biopsy/incisional biopsy in cosmetically sensitive sites
    • Deep shave biopsy
  • Findings:
    • Replacement of basal keratinocytes by nests of atypical melanocytes
    • No basement membrane invasion (if present, indicates progression to invasive melanoma)
    • Changes of chronic sun damage:
      • Epidermal atrophy
      • Inflammatory dermal infiltrates
      • Effacement of rete ridges

Lentigo maligna:
A nest of atypical melanocytes can be noted. The basement membrane is intact. Therefore, this lesion is lentigo maligna (in situ).

Image: “Lentigo maligna” by Sheliza Halani et al. License: CC BY 4.0

Management and Prognosis

Management

Surgical excision:

  • 1st line treatment
  • Procedures:
    • Wide local excision:
      • Margins of 5–10 mm should be obtained.
      • For small lesions with well-delineated borders
    • Staged excisions:
      • Involves histologic examination of the permanent sections
      • Excisions are performed until negative margins are obtained.
      • For large lesions (> 1 cm on the head/neck and > 2 cm on trunk/extremities)
      • For lesions with ill-defined borders 
    • Mohs micrographic surgery:
      • Staged excision that involves examination of frozen sections
      • May not be as reliable as staged excision technique for lentigo maligna

Nonsurgical:

  • Reserved for:
    • Elderly frail patients
    • Patients refusing surgery
    • Large lesions in cosmetically sensitive areas where problematic reconstruction is expected
  • Includes:
    • Radiotherapy
    • Laser
    • Cryosurgery
    • Topical imiquimod

Patient education:

  • Protection from ultraviolet radiation (sunblock, clothing)
  • Self-examination of the skin

Prognosis

  • Up to 20% of presumed lentigo maligna biopsies are found to have invasive melanoma.
  • Can take from < 10 to > 50 years for lentigo maligna to progress to lentigo maligna melanoma.
  • 6%–9% recurrence rate after wide excision
  • In the absence of progression to lentigo maligna melanoma, lentigo maligna does not shorten life expectancy.
  • No disease-related deaths when complete excision is achieved

Differential Diagnosis

  • Solar lentigo: macular lesions with irregular margins and uniform brown pigmentation on sun-exposed skin similar to lentigo maligna. Biopsy of these lesions shows no nesting of atypical melanocytes. Solar lentigo is benign and does not require treatment.
  • Melanoma: a skin malignancy derived from the malignant transformation of melanocytes. The most common type of melanoma is superficial spreading melanoma, which usually presents as an irregular macule/patch. On histopathologic examination, atypical melanocytes would be detected in the dermis. Lentigo maligna can progress to lentigo maligna melanoma. The mainstay of treatment is surgical excision.
  • Atypical nevus: a benign melanocytic neoplasm that mimics lentigo maligna in appearance as it may be asymmetric and > 6 mm with color variegation. Dermoscopic examination and biopsy are needed to differentiate. Does not require excision if the diagnosis is certain.
  • Seborrheic keratosis: a benign neoplasm consisting of immature keratinocytes occurring commonly in the elderly. This condition is demarcated, waxy, and has a stuck-on appearance. A biopsy will show abnormal keratinocytes versus melanocytes. Dermoscopy would show cysts and fissures. This neoplasm does not require treatment.
  • Actinic keratosis: a precancerous lesion that affects sun-exposed areas (e.g., scalp and hands) in elderly patients. This condition appears as a scaly, slightly elevated lesion that should be excised or treated topically to prevent invasive squamous cell carcinoma development. The only way to differentiate from lentigo maligna is by a biopsy that shows atypical keratinocytes in the basal layer.
  • Dermatofibroma: a common mesenchymal growth of the skin where skin fibroblasts are the primary constituents. This condition usually presents as a firm, indurated, mobile nodule measuring about 0.5–1 cm in size. Upon lateral compression, a dimple-like depression is seen in the overlying skin (“buttonhole” sign). Does not require treatment, but can be surgically excised if bothersome to the patient.

References

  1. Charifa A. (2020). Lentigo Maligna Melanoma. Retrieved February 24, 2021, from https://www.statpearls.com/articlelibrary/viewarticle/24188/
  2. Cohen L.M. (1995). Lentigo maligna and lentigo maligna melanoma. J Am Acad Dermatol. 1995 Dec;33(6):923-36; quiz 937-40.
  3. Sober A. J., Olbricht S., Hong A.M. (2019). Lentigo maligna: Clinical manifestations, diagnosis, and management. Retrieved February 24, 2021, from https://www.uptodate.com/contents/lentigo-maligna-clinical-manifestations-diagnosis-and-management

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