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Lentigo maligna
Evidence Levels: A Double-blind study B Clinical trial ≥ 20 subjects C Clinical trial < 20 subjects D Series ≥ 5 subjects E Anecdotal case reports
Lentigo maligna (LM) is a subtype of preinvasive intraepidermal melanoma (viewed by some as melanoma in situ) that classically presents as widespread pigmented patches of atypical melanocytes in the background of longstanding sun damage. The lifetime risk of LM progressing to invasive lentigo maligna melanoma (LMM) varies from 2.2%–4.7%, depending on patient age at diagnosis. LMM represents 4%–15% of all melanomas, and its incidence is increasing at a greater rate than any other melanoma subtype. LM has traditionally been challenging to diagnose because it is difficult to distinguish non-malignant atypical melanocytic hyperplasia from melanoma in situ (MIS) in chronically sun-damaged skin. Treatment of LM remains complex, with recurrence rates that remain high (2%–50%) due to subclinical extension.
Management Strategy
Successful management of LM depends on early diagnosis and definitive removal. Confirmatory biopsy is necessary before definitive treatment. The use of a Wood lamp and dermoscopy may help to determine the perimeter of the lesion. Excisional biopsy of the entire lesion is ideal in order to ascertain its maximum depth. However, the lesion tends to be large (>1 cm) due to its propensity for extensive radial growth before vertical growth into the dermis. Treatment is primarily surgical, although eradication by other methods may be considered. Patients with a history of LM should have periodic full-body skin examinations to determine recurrence as well as new skin malignancies, and they need sun avoidance advice.
Diagnosis and treatment of early melanoma
NIH Consensus Statement. 1992; 10: 1–26.
Biopsy of sufficient depth is critical for diagnosis and management of pigmented lesions. Punch, saucerization, excision, or incisional biopsy may be acceptable. On microscopic examination, LM is characterized by increased numbers of atypical melanocytes at the epidermal–dermal junction, which may be solitary or arranged in nests but do not invade the dermis. Evaluation should include a personal and family history, complete skin examination, and palpation of regional lymph nodes. Blood tests or imaging studies are not indicated.
From the Academy Guidelines of care for the management of primary cutaneous melanoma
Swetter SM, Tsao H, Bichakjian CK, et al. J Amer Acad Dermatol 2019; 80: 208–50.
Management guidelines for these lesions were recently updated by the Academy in the 2019 JAAD article referenced above.
Diagnosis and treatment of early melanoma
NIH Consensus Statement. 1992; 10: 1–26.
Current recommendations are based on the National Institutes of Health (NIH) consensus for MIS, which suggests excision of the lesion or biopsy site with a margin of 0.5 cm of clinically normal skin and layer of subcutaneous tissue. In general, margins of 0.5–1.0 cm are suggested for LM where feasible. A Wood lamp may be useful in defining subclinical extension. Reflectance confocal microscopy (RCM) may also improve diagnostic accuracy of LM by identifying optimal biopsy sites. RCM may assist in presurgical mapping, intraoperative margin assessment, assessing response to non-surgical therapies, and monitoring for recurrence. Accurate determination of margins is key because LM is likely to recur after inadequate excision.
Usefulness of the staged excision for lentigo maligna and lentigo maligna melanoma: the “square” procedure
Johnson TM, Headington JT, Baker SR, et al. J Am Acad Dermatol 1997; 37: 758–64.
With this technique, a margin of 0.5–1.0 cm is outlined with angled corners to facilitate processing. A peripheral strip of tissue 2–4 cm wide is excised and processed for evaluation of permanent sections. The residual tumor is subsequently excised in a directed fashion based on mapping. There were no recurrences in 35 patients at 2 years.
Ten years’ experience using the Johnson square procedure for lentigo maligna
Smith H, Olabi B, Lam M, et al. Brit J Dermatol 2019; 181: 602–4.
In the UK, between July 2007 and July 2017, 44 biopsy-confirmed, ill-defined head and neck LM/LMM from 43 patients (median age 75 years [range 49–92]; male-to-female ratio 27:16) underwent the Johnson square procedure. Of these lesions, 25 were cleared with one stage, 15 with two stages, one with three stages, and three with four stages (1 lesion extended beyond the mucosal surface of the left inner canthus making margin control impossible). Therefore, 73% (32 lesions) required more than a standard 5-mm margin to clear. Clearance rate reported as 97.7%. No patients with completely excised lesions were rereferred during the 10-year study period.
Mohs micrographic surgery is accurate 95.1% of the time for melanoma in situ: a prospective study of 167 cases
Bene NI, Healy C, Coldiron BM. Dermatol Surg 2008; 34: 660–4.
Patients ( n = 116) with MIS in sun-exposed skin of LMM type were treated by Mohs micrographic surgery (MMS) with subsequent evaluation of the final margin with paraffin-embedded sections that were cut en face over a period of 12 years (mean follow-up, 50 months; median 48 months; 594.5 patient-years). The clearance rate by MMS technique using frozen sections was 94.1% for the MIS LM type. The cure rate was 99.0% for the MIS LM type.
MMS is a viable option for treatment of MIS that may increase cure rate and reduce the size of the defect, especially in cosmetically and functionally sensitive areas.
Conventional surgery compared with slow Mohs micrographic surgery in the treatment of lentigo maligna: a retrospective study of 62 cases
Hilari H, Llorca D, Traves V, et al. Actas Dermosifiliogr 2012; 103: 614–23.
A review of the clinical records of patients with LM of the head treated definitively with conventional surgical excision or slow MMS. Surgical margins larger than 0.5 cm were required in 69.2% of recurrent LM and in 26.5% of primary LM. Factors associated with the need for wider margins were prior treatment that might have interfered with the clinical delineation of the border, lesions in the center of the face, and skin phototypes III–V. Surgical margins of 0.5 cm are inadequate for the treatment of a considerable number of LM lesions located on the head, particularly if these are recurrent. Slow MMS using paraffin-embedded sections appears to be the treatment of choice in such cases, particularly for recurrent lesions or lesions with poorly defined borders or possible subclinical extension.
A potential disadvantage of relying on ‘slow Mohs’ is the amount of time added to each procedure. In addition, the technique depends on off-site tissue processing and interpretation, thereby magnifying the possibility of error.
Upstaging of melanoma in situ and lentigo maligna [ on sun-damaged skin ] treated with Mohs micrographic surgery rarely results in additional surgical management
Levoska MA, Schmults CD, Waldman AH. Arch Dermatol Res 2020; doi: 10.1007/s00403-020-02034-9.
A retrospective chart review of 117 MIS/LM lesions treated with MMS at Brigham and Women’s Hospital revealed a low rate of tumor upstaging (8.5% or 10/117) and only 1.7% (2/117) required wide local incision and sentinel lymph node.
Five-year outcomes of wide excision and Mohs micrographic surgery for primary lentigo maligna in an academic practice cohort
Hou JL, Reed KB, Knudson RM, et al. Dermatol Surg 2015; 41: 211–8.
In total, 423 LM lesions were treated with either wide excision (269) or Mohs (154). Recurrence rates were 1.9% for the Mohs-treated group and 5.9% for the wide excision group. The study concluded that Mohs surgery may offer increased cure rates and avoid the need for repeat surgery and thus may be the preferred treatment for LM.
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