Lentigo Maligna

What lentigo maligna is

Melanocytes are the pigment cells at the base of the epidermis, the outer layer of skin. In lentigo maligna, abnormal melanocytes multiply along this layer and spread sideways, sometimes for many years, without crossing into the deeper dermis. Because they have not invaded, the cancer cannot spread elsewhere at this stage. That is what "in situ" means. It is one subtype of melanoma in situ.

If the cells break through into the dermis, it becomes lentigo maligna melanoma (LMM), an invasive melanoma. Estimates of how often this happens vary widely, but the lifetime risk is thought to be modest, and progression usually takes years. Because nobody can predict which patches will progress, treatment is recommended.

Causes and risk factors

The main cause is cumulative ultraviolet (UV) exposure over decades, rather than intermittent sunburns.

• age over 60
• fair skin that burns easily, light hair and eyes
• outdoor work or hobbies
• many sun spots and actinic keratoses, signs of heavy sun damage
• previous skin cancer
• weakened immune system

What lentigo maligna looks like

• a flat patch, not raised, usually larger than 6 mm and sometimes several centimeters
• irregular, notched or blurred borders
• uneven color: shades of tan, brown, dark brown or black, sometimes with pink, gray or white areas where parts regress
• slow growth over months to years
• no symptoms: it does not itch or hurt

Signs that suggest invasion into lentigo maligna melanoma include a raised area, a lump, thickening, a blue-black nodule, bleeding or crusting.

Lentigo maligna vs age spots and other lookalikes

Telling these apart can be difficult even for experts. Any facial pigmented spot that is changing or looks different from the others deserves a dermatologist's assessment, and should not be frozen or lasered without a diagnosis.

Diagnosis

1. Full skin examination and history of how the spot has changed.
2. Dermoscopy: a magnified, lit view showing features such as uneven pigmentation around hair follicles and angular, rhomboid structures.
3. Reflectance confocal microscopy in some specialist centers, to map the edges without cutting.
4. Biopsy: a broad shave or incisional biopsy, sometimes several, because a small sample can miss the most abnormal part. The pathologist confirms in situ disease or looks for invasion.

If invasion is found, the case is managed as invasive melanoma, with tumor thickness (Breslow depth) guiding staging and further tests.

Treatment

Surgery (first choice)

The goal is complete removal with a clear margin. Lentigo maligna is tricky because abnormal cells often extend well beyond the visible edge into sun-damaged skin. Standard margins for melanoma in situ are about 5 to 10 mm, and lentigo maligna often needs wider.

• Staged excision ("slow Mohs" or "square" procedure): the edges are removed and examined fully in the lab before the center is cut out and the wound repaired. This takes several days but gives the lowest recurrence.
• Mohs surgery with special stains: the margins are checked layer by layer on the same day.
• Wide local excision: standard surgery with a measured margin, used when the area is not cosmetically sensitive.

Facial repair may involve a skin flap or graft.

Non-surgical options

When surgery is not possible, because of the size, location or the person's health:

• Imiquimod cream: an immune-stimulating cream applied for several weeks. It is off-label for lentigo maligna and has higher recurrence than surgery, but it is a reasonable choice for some people.
• Radiation therapy: effective for large lesions in older adults.
• Observation: sometimes chosen for frail elderly people with limited life expectancy, given the slow progression.

Freezing (cryotherapy) and laser are not recommended because they can leave cells behind and hide recurrence.

Follow-up and prevention

Recurrence happens most often at the edges, sometimes years later, so regular skin checks are needed, along with monthly self-checks of the scar and surrounding skin. People with one lentigo maligna are at higher risk of other skin cancers, including basal cell carcinoma.

Daily broad-spectrum sunscreen (SPF 30 or higher), a wide-brimmed hat and avoiding midday sun reduce further damage at any age.

Frequently asked questions

Is lentigo maligna cancer?

Yes. Lentigo maligna is melanoma in situ: the abnormal cells are cancerous but confined to the top layer of skin. At this stage it cannot spread to other parts of the body, and complete removal cures it.

How fast does lentigo maligna grow?

Usually very slowly, spreading sideways over years or even decades. A minority eventually become invasive lentigo maligna melanoma. Because the timing cannot be predicted for each person, treatment is recommended once it is diagnosed.

How can I tell lentigo maligna from an age spot?

Age spots are usually uniformly tan or brown with smooth borders and stay stable. Lentigo maligna tends to have several shades of brown or black, an irregular border, and slowly gets bigger or darker. Only dermoscopy or a biopsy can confirm it.

What is Hutchinson's melanotic freckle?

It is an older name for lentigo maligna, after Jonathan Hutchinson, who described it in the 1890s. It refers to the same slowly enlarging, flat, pigmented melanoma in situ found on sun-damaged skin of older adults.

Does lentigo maligna come back after surgery?

It can, especially at the edges, because abnormal cells may extend invisibly into nearby sun-damaged skin. Recurrence is lowest after staged excision or Mohs surgery with full margin checking. Regular follow-up skin checks catch returning disease early.