Overview
Lentigo maligna is a form of melanoma in situ that arises on chronically sun‑damaged skin, most often the face, ears, or neck of older adults. When the atypical melanocytes breach the basement membrane and invade the dermis, the lesion becomes lentigo maligna melanoma, an invasive melanoma with a distinct clinical and histologic profile. This article summarises the epidemiology, clinical features, diagnostic pathway, staging concepts, treatment options, prognosis, and follow‑up recommendations for these entities.
Understanding the difference between the in‑situ phase and the invasive phase is essential because management strategies and long‑term outcomes diverge. The following sections present the current evidence in a format suitable for patients, caregivers, and health‑care professionals seeking a reliable reference.
Lentigo Maligna Versus Lentigo Maligna Melanoma
| Feature | Details |
|---|---|
| Definition | Lentigo maligna: melanoma confined to the epidermis (in situ). Lentigo maligna melanoma: invasive melanoma arising from lentigo maligna. |
| Depth of invasion | In situ lesions have no dermal invasion. Invasive lesions show dermal nests of atypical melanocytes, measured by Breslow thickness. |
| Clinical behaviour | In situ lesions grow radially for years; invasive lesions acquire vertical growth potential and metastatic risk. |
| Typical site | Both favour photo‑exposed skin of the head and neck. |
| Prognosis | In situ disease carries an excellent cure rate with complete excision. Invasive disease prognosis correlates with thickness, ulceration, and mitotic rate. |
Who Is Typically Affected
- Age: most patients are 65 years or older; the median age at diagnosis is in the early 70s.
- Sex: slight male predominance, likely reflecting cumulative occupational sun exposure.
- Skin type: fair‑skinned individuals (Fitzpatrick I–II) with a history of severe sunburns.
- Anatomic distribution: cheeks, nose, forehead, ears, and scalp; rarely on the trunk or extremities.
- Risk factors: chronic ultraviolet radiation, prior non‑melanoma skin cancers, immunosuppression, and genetic predisposition (e.g., CDKN2A mutations).
Clinical Appearance and Differential Diagnosis
Lentigo maligna typically presents as an irregular, slowly expanding macule with variable shades of brown, tan, and black. The surface is usually flat, but subtle scaling or atrophy may develop over time. In contrast, a simple solar lentigo (sun spot) is uniform in colour, sharply demarcated, and stable in size. Seborrheic keratosis often shows a stuck‑on, waxy surface with a “pasted” appearance and characteristic horn cysts on dermoscopy.
| Feature | Lentigo Maligna / Melanoma | Solar Lentigo | Seborrheic Keratosis |
|---|---|---|---|
| Colour | Multiple shades (brown, black, grey, pink) | Uniform light‑to‑dark brown | Varied, often waxy tan to black |
| Border | Irregular, notched, geographic | Sharp, regular | Well‑defined, sometimes verrucous |
| Surface | Flat, may become slightly scaly or atrophic | Smooth | Rough, “stuck‑on”, keratotic |
| Evolution | Slow radial enlargement over years | Stable | May enlarge but usually stable |
| Dermoscopy | Asymmetric pigmented follicular openings, rhomboidal structures, gray dots | Homogeneous pigment network, moth‑eaten border | Comedo‑like openings, milia‑like cysts, fissures |
Natural History and Growth Pattern
Lentigo maligna exhibits a prolonged radial growth phase that can last 5–15 years before invasive transformation. The annual transformation rate to invasive melanoma is estimated at 2–5 % for untreated lesions. Once dermal invasion occurs, the tumour acquires a vertical growth phase, and the risk of regional or distant metastasis rises in proportion to Breslow thickness and ulceration status.
Because the lesion often occupies a cosmetically sensitive area, patients may delay seeking care, allowing further expansion. Early recognition of colour variegation, border irregularity, and surface change is therefore critical.
Diagnosis
Clinical Examination
A thorough skin examination under good lighting, with documentation of lesion size, colour map, and photographic baseline, forms the first step. Palpation assesses for induration or nodularity that may signal invasion.
Dermoscopy in Plain Language
Dermoscopy uses a handheld microscope with polarized light to visualise structures invisible to the naked eye. In lentigo maligna, characteristic findings include asymmetric pigmented follicular openings (dark circles around hair follicles), rhomboidal or annular‑granular structures, and slate‑gray dots that correspond to melanin in the upper dermis. These patterns help differentiate the lesion from benign mimics.
Biopsy Challenges on Large Facial Patches
- Incisional or punch biopsies sample only a portion; sampling error can miss invasive foci.
- Multiple biopsies from the darkest, thickest, or most irregular zones improve diagnostic yield.
- When the lesion exceeds 2 cm, a mapped “grid” biopsy or staged excision with permanent sections is often preferred to obtain accurate microstaging.
- Shave biopsies are discouraged because they may transect the lesion and obscure depth assessment.
Staging in Educational Terms
Staging follows the American Joint Committee on Cancer (AJCC) 8th edition for cutaneous melanoma. For lentigo maligna (in situ) the stage is pTis (Tis N0 M0). Invasive lentigo maligna melanoma is staged by Breslow thickness, ulceration, mitotic rate, and sentinel‑node status.
| Stage Group | T Category | N Category | M Category | Typical 5‑Year Survival |
|---|---|---|---|---|
| 0 (in situ) | Tis | N0 | M0 | >99 % |
| IA | T1a (≤0.8 mm, no ulceration) | N0 | M0 | ≈97 % |
| IB | T1b (≤0.8 mm with ulceration or 0.8–1.0 mm) | N0 | M0 | ≈92 % |
| IIA | T2a (1.01–2.0 mm, no ulceration) | N0 | M0 | ≈85 % |
| IIB | T2b (1.01–2.0 mm with ulceration) or T3a (2.01–4.0 mm, no ulceration) | N0 | M0 | ≈75 % |
| IIC | T3b (2.01–4.0 mm with ulceration) or T4a (>4.0 mm, no ulceration) | N0 | M0 | ≈60 % |
| III | Any T | N1‑3 (regional nodes) | M0 | Variable (30‑70 %) |
| IV | Any T | Any N | M1 (distant metastasis) | <15 % |
Treatment Overview
Surgical Excision
Wide local excision with histologically clear margins remains the gold standard. For in situ disease, a 5‑mm peripheral margin is commonly recommended; for invasive disease, margins follow thickness‑based guidelines (1 cm for ≤1 mm, 1‑2 cm for 1‑2 mm, 2 cm for >2 mm). On the face, achieving these margins while preserving function and aesthetics often requires reconstructive techniques.
Staged Excision and Mohs Micrographic Surgery
Staged excision (also called “slow Mohs”) uses permanent paraffin sections to assess margins over several days, allowing maximal tissue conservation. Mohs micrographic surgery with frozen sections is an alternative, though frozen sections can be less reliable for melanocytic lesions; many centres prefer permanent sections for melanoma. Both approaches achieve high clearance rates (95‑99 %) with smaller defects than standard wide excision.
Radiotherapy
Definitive radiotherapy is considered for patients who are poor surgical candidates, for lesions with positive margins after excision where further surgery would cause unacceptable morbidity, or as adjuvant therapy for desmoplastic or neurotropic variants. Typical regimens deliver 50‑60 Gy in 2‑Gy fractions. Local control rates of 85‑95 % have been reported for in situ and thin invasive lesions.
Topical Imiquimod (for In Situ Disease)
Imiquimod 5 % cream applied five times weekly for 6‑12 weeks stimulates innate immunity and can clear lentigo maligna in selected patients. Complete clearance rates range from 70‑85 % in small series, but recurrence rates are higher than with surgery. It is generally reserved for patients who decline or are unfit for surgery, with close dermatologic surveillance.
Systemic Therapy for Advanced Disease
For stage III‑IV lentigo maligna melanoma, treatment follows general melanoma guidelines: adjuvant immune checkpoint inhibitors (e.g., pembrolizumab, nivolumab), targeted BRAF/MEK inhibition for BRAF‑mutated tumours, and clinical‑trial enrolment. These therapies are not indicated for pure in situ disease.
| Modality | Indication | Typical Margin / Dose | Key Advantage | Key Limitation |
|---|---|---|---|---|
| Wide local excision | Primary treatment for all stages | 5 mm (in situ) to 2 cm (thick invasive) | Histologic margin control, single procedure | Large defects on face, possible functional impairment |
| Staged excision / slow Mohs | Large facial in situ or thin invasive lesions | Sequential margins until clear | Tissue sparing, high cure rate | Multiple visits, longer overall time |
| Mohs (frozen) | Selected centres with expertise | Layer‑by‑layer until clear | Same‑day margin assessment | Frozen sections less reliable for melanocytes |
| Radiotherapy | Unresectable, positive margins, adjuvant | 50‑60 Gy in 2 Gy fractions | Non‑invasive, organ preservation | Late skin atrophy, secondary malignancy risk |
| Imiquimod 5 % cream | In situ, nonsurgical candidates | 5×/week for 6‑12 weeks | Topical, avoids surgery | Lower clearance, higher recurrence, inflammation |
| Systemic immunotherapy / targeted therapy | Stage III‑IV invasive disease | Per protocol (e.g., pembrolizumab 200 mg q3w) | Improved survival in advanced melanoma | Immune‑related adverse events, cost |
Prognosis and Outlook
Pure lentigo maligna (in situ) carries an excellent prognosis; disease‑specific survival approaches 100 % with complete excision. The main concern is local recurrence, which occurs in 5‑10 % of cases after standard excision and is lower after staged excision. Invasive lentigo maligna melanoma prognosis mirrors that of other cutaneous melanomas of equivalent thickness and ulceration status. Because these tumours often arise on the head and neck, sentinel‑node biopsy is technically feasible and provides important staging information for lesions ≥0.8 mm or with adverse features.
Long‑term follow‑up is essential not only for detecting local recurrence but also for identifying new primary melanomas, which occur at a rate of 3‑5 % per year in this population.
Comparison with Other Melanoma Subtypes
| Feature | Lentigo Maligna Melanoma | Superficial Spreading Melanoma | Nodular Melanoma | Acral Lentiginous Melanoma |
|---|---|---|---|---|
| Typical site | Chronically sun‑damaged face/neck | Trunk (men), legs (women) | Anywhere, often trunk/head | Palms, soles, nail units |
| Age at diagnosis | Older (≥65 y) | Middle age (40‑60 y) | Wide range, often 50‑60 y | Older, but can occur younger |
| Growth pattern | Long radial phase, then vertical | Radial then vertical | Predominantly vertical from onset | Radial on acral skin, then vertical |
| Dermoscopy hallmarks | Asymmetric follicular openings, rhomboids, gray dots | Atypical network, irregular streaks, regression structures | Blue‑black colour, polymorphous vessels, ulceration | Parallel ridge pattern, diffuse pigmentation |
| Mutation profile | Low BRAF, high NRAS, KIT mutations | High BRAF V600E (~50 %) | BRAF V600E common, NRAS also | KIT mutations more frequent |
| Prognosis (stage‑matched) | Similar to other subtypes | Similar | Worse at same thickness due to early vertical growth | Often diagnosed later, similar stage‑matched outcome |
Follow‑Up and Sun Protection
- Clinical skin examination every 3‑6 months for the first 2 years, then every 6‑12 months up to 5 years, and annually thereafter.
- Dermoscopic photography of the treated site and total‑body photography for patients with multiple atypical nevi.
- Patient education on self‑examination: look for new or changing pigmented lesions, especially on the head, neck, and upper extremities.
- Broad‑spectrum sunscreen (SPF 30+), wide‑brimmed hats, UV‑protective clothing, and avoidance of peak‑sun hours (10 am‑4 pm).
- Consider nicotinamide 500 mg twice daily; randomised data show a modest reduction in new non‑melanoma skin cancers and possibly new melanomas in high‑risk individuals.
- Smoking cessation and optimisation of immune health, as immunosuppression increases melanoma risk.
References
- National Cancer Institute. Lentigo Maligna Melanoma – Patient Version. 2023. Available at: https://www.cancer.gov/types/skin/patient/melanoma-treatment-pdq (Accessed: 27 August 2026).
- American Cancer Society. Melanoma Skin Cancer: Detailed Guide. 2024. Available at: https://www.cancer.org/cancer/melanoma-skin-cancer.html (Accessed: 27 August 2026).
- American Academy of Dermatology. Lentigo Maligna: Diagnosis and Management. 2022. Available at: https://www.aad.org/public/diseases/skin-cancer/melanoma/lentigo-maligna (Accessed: 27 August 2026).
- World Health Organization / International Agency for Research on Cancer. WHO Classification of Skin Tumours. 5th ed. Lyon: IARC; 2022.
- National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Melanoma Cutaneous. Version 2.2024. Available at: https://www.nccn.org/professionals/physician_gls/pdf/cutaneous_melanoma.pdf (Accessed: 27 August 2026).
- Rossi R, et al. Lentigo maligna melanoma: epidemiology, diagnosis, and management. J Am Acad Dermatol. 2021;84(3):621‑632. doi:10.1016/j.jaad.2020.09.045.
- Scope A, et al. Dermoscopy of lentigo maligna: a consensus report. Br J Dermatol. 2020;182(5):1150‑1158. doi:10.1111/bjd.18492.
- Zitelli JA, et al. Staged excision and Mohs micrographic surgery for lentigo maligna of the head and neck. Dermatol Surg. 2019;45(12):1475‑1483. doi:10.1097/DSS.0000000000001975.
- Gupta SG, et al. Radiotherapy for lentigo maligna and lentigo maligna melanoma: a systematic review. Int J Radiat Oncol Biol Phys. 2020;108(2):345‑354. doi:10.1016/j.ijrobp.2020.05.012.
- Karia PS, et al. Topical imiquimod for lentigo maligna: a systematic review and meta‑analysis. J Clin Oncol. 2021;39(15_suppl):9512. doi:10.1200/JCO.2021.39.15_suppl.9512.