Lentigo Maligna Melanoma: Slow‑Growing Skin Cancer on Sun‑Damaged Sites

Lentigo maligna melanoma (LMM) is a distinct subtype of melanoma that typically arises on chronically sun-damaged skin, especially on the face, ears, neck, and forearms. It is known for its slow horizontal growth phase, often remaining in situ for years before becoming invasive. This article explores the nature of lentigo maligna melanoma, the related concept of lentiginous melanoma, and answers the common question: is lentigo maligna a melanoma? Understanding these nuances is crucial for early detection and appropriate management.

Lentigo maligna melanoma accounts for about 5–15% of all melanomas, with higher incidence in elderly individuals with long-term sun exposure. The early stage, called lentigo maligna (LM), is considered a melanoma in situ, meaning the abnormal melanocytes are confined to the epidermis. Over time, if untreated, it can progress to invasive lentigo maligna melanoma, where cells penetrate the dermis. This slow progression provides a window for diagnosis and treatment, making awareness of its signs vital.

The term “lentiginous melanoma” is sometimes used interchangeably with lentigo maligna melanoma, though it more broadly describes melanomas with a lentiginous growth pattern—where melanocytes grow in a single-file pattern along the basal layer. Lentigo maligna melanoma is the prototype of lentiginous melanoma, but other types like acral lentiginous melanoma also exist. So, when asking “is lentigo maligna a melanoma?” the answer is yes: lentigo maligna is a melanoma in situ, and once invasive, it becomes lentigo maligna melanoma. It is a true melanoma, albeit a slow-growing variant.

Characteristics of Lentigo Maligna Melanoma

Lentigo maligna melanoma often presents as a slowly enlarging, irregularly pigmented macule or patch on sun-exposed skin. It can be brown, black, or even hypopigmented, and its borders are typically ill-defined. The lesions can reach several centimeters in diameter and are often mistaken for age spots or seborrheic keratoses. Over years, a raised nodule may develop, indicating invasion. Dermoscopy reveals features like asymmetric pigmented follicular openings, rhomboidal structures, and annular-granular patterns. Recognizing these signs is essential for dermatologists to differentiate LMM from other pigmented lesions.

The slow growth of lentiginous melanoma is attributed to its predominantly radial growth phase. Unlike nodular melanoma, which grows rapidly downward, LMM spends years spreading horizontally. This is why it is often called a “slow-growing” melanoma. However, once it enters the vertical growth phase, it can behave aggressively like any other melanoma. Risk factors include advanced age, cumulative sun exposure, fair skin, and a history of non-melanoma skin cancers. Patients with lentigo maligna often have multiple actinic keratoses and solar lentigines.

• Lentigo maligna melanoma is most common on the face, especially the cheeks and nose.
• It may be misdiagnosed as solar lentigo, pigmented actinic keratosis, or lentiginous melanoma mimics.
• Biopsy with histopathology is required for definitive diagnosis, showing atypical melanocytes along the basal layer with follicular involvement.

Diagnosis and Treatment Approaches

Diagnosis begins with a full skin examination and dermoscopy. Any suspicious lesion should undergo a punch or excisional biopsy with narrow margins. Histologically, lentigo maligna shows a proliferation of atypical melanocytes along the dermal-epidermal junction, often extending down hair follicles. The presence of nests, pagetoid spread, and dermal invasion confirms invasive lentigo maligna melanoma. The Breslow depth, ulceration, and mitotic rate determine staging and prognosis. Lentiginous melanoma patterns are also noted in other sites, such as acral areas.

Treatment for lentigo maligna melanoma includes surgical excision with appropriate margins (0.5–1 cm for in situ, 1–2 cm for invasive) as per National Comprehensive Cancer Network guidelines. For large lesions on the face, Mohs micrographic surgery is often preferred to maximize tissue preservation and ensure clear margins. Alternative treatments for lentigo maligna include imiquimod cream, radiation therapy, or cryotherapy for those who cannot undergo surgery. However, these non-surgical options have higher recurrence rates. Regular follow-up is mandatory due to risk of recurrence and development of new primary melanomas.

Prognosis for lentigo maligna melanoma is generally favorable when detected early. The 10-year survival for stage I LMM is over 90%, similar to other melanomas of equivalent depth. However, because it often occurs in elderly patients with comorbidities, treatment decisions must be individualized. The question “is lentigo maligna a melanoma?” is unequivocally yes, but its indolent course should not lead to complacency. Continued sun protection and surveillance are essential for all patients with a history of lentiginous melanoma.

In summary, lentigo maligna melanoma is a slow-growing but potentially deadly skin cancer that arises on sun-damaged skin. Understanding its features, the concept of lentiginous melanoma, and answering “is lentigo maligna a melanoma?” with a clear yes, empowers patients and clinicians to take action. Regular skin checks and prompt biopsy of suspicious lesions remain the cornerstone of management. By raising awareness, we can improve outcomes for those affected by this distinctive melanoma.