Lentigo maligna (also known as Hutchinson melanotic freckle) is melanoma in situ. This type of precancerous lesion may progress to lentigo maligna melanoma.
- 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.
- 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
- 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
- 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
- Amount of sun exposure
- Other skin cancers
- Family history of melanoma
- Hereditary diseases
- Complete/thorough skin exam should be performed.
- Synchronous malignant and premalignant lesions are not uncommon in individuals with extensive sun damage to the skin.
- 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
- Gold standard for lentigo maligna diagnosis
- Sample obtained via:
- Excisional biopsy (ideal)
- Punch biopsy/incisional biopsy in cosmetically sensitive sites
- Deep shave biopsy
- 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
Management and Prognosis
- 1st line treatment
- 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
- Wide local excision:
- Reserved for:
- Elderly frail patients
- Patients refusing surgery
- Large lesions in cosmetically sensitive areas where problematic reconstruction is expected
- Topical imiquimod
- Protection from ultraviolet radiation (sunblock, clothing)
- Self-examination of the skin
- 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
- 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.
- Charifa A. (2020). Lentigo Maligna Melanoma. Retrieved February 24, 2021, from https://www.statpearls.com/articlelibrary/viewarticle/24188/
- Cohen L.M. (1995). Lentigo maligna and lentigo maligna melanoma. J Am Acad Dermatol. 1995 Dec;33(6):923-36; quiz 937-40.
- 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