Acral Lentiginous Melanoma (ALM): Causes, Symptoms, Treatment

Acral Lentiginous Melanoma: Unique Type of Skin Cancer

Acral lentiginous melanoma (ALM) is a rare but serious subtype of melanoma that develops on the palms of the hands, soles of the feet, or under the nails (subungual areas). Unlike other melanomas that are often linked to sun exposure, ALM typically appears in areas that receive little to no sun exposure, making it a particularly tricky type of skin cancer to identify and understand.

While ALM accounts for only 2-3% of all melanomas in the general population, it is the most common type of melanoma in people with darker skin tones, including African Americans, Hispanics, and Asians. This unique pattern makes ALM a critical health concern for communities that traditionally face lower risks of other skin cancers but higher risks of this specific subtype.

What Makes ALM Different?

Location of Acral Lentiginous Melanoma (ALM)

ALM specifically develops in three main areas:

1. Plantar surfaces (soles of the feet) – The most common site, accounting for about 76% of cases
2. Palmar surfaces (palms of the hands) – About 8% of cases
3. Subungual areas (under fingernails or toenails) – About 16% of cases, with the thumb and great toe being involved in 92% of nail cases

Not Sun-Related

Here’s what surprises many people: ALM is not caused by UV radiation or sun exposure. This is fundamentally different from other melanoma subtypes like superficial spreading melanoma or nodular melanoma. Scientists believe ALM develops through different biological pathways, which explains why it affects all skin types equally and why it behaves differently than sun-induced melanomas.

Symptoms of Acral Lentiginous Melanoma

The “CUBED” Rule for Acral Surfaces

Because the traditional “ABCDE” rule (Asymmetry, Border, Color, Diameter, Evolving) doesn’t work as well for palms, soles, and nails, doctors use a special acronym called “CUBED” to spot ALM early:

Specific Signs by Location

On Palms and Soles:

• A flat, dark brown to black spot with irregular borders
• A streak or patch that follows the natural skin lines (dermatoglyphics)
• Areas that look like bruises but don’t fade
• Thick, callus-like areas that grow or change
• Ulcers or open sores that won’t heal

Under Nails (Subungual):

• A dark brown or black streak running from the cuticle to the nail tip
• Hutchinson sign: Dark pigment spreading from under the nail onto the surrounding skin (cuticle or nail fold) – this is a major red flag
• Nail splitting, destruction, or lifting from the nail bed
• A dark patch that doesn’t move when the nail grows
• Bleeding under the nail without trauma

The “ABCDEF” Rule for Nail Melanoma

For nail-specific concerns, doctors also use:

• A: Age (peak occurrence 50-70 years) and African, Asian, or Native American heritage
• B: Brown-black band wider than 3mm with blurred borders
• C: Change or no change at all despite active treatment
• D: Digit involvement (thumb, big toe, or index finger most common)
• E: Extension of pigment into surrounding skin (Hutchinson sign)
• F: Family or personal history of melanoma

Who Is at Risk?

Unlike other skin cancers where risk increases with fair skin and sun exposure, ALM risk factors are different:

Higher Risk Groups:

• All skin types equally – This is crucial: ALM affects dark skin just as often as light skin
• People of African, Asian, Hispanic, and Native American descent – ALM represents the majority of melanomas in these populations
• Older adults – Risk increases with age, peaking between 60-70 years
• Men and women – Both sexes are affected, though some studies show slight male predominance

How Doctors Diagnose ALM

Step 1: Clinical Examination

Your doctor will examine the suspicious area closely, looking at color patterns, borders, and any signs of spread.

Step 2: Dermoscopy (Skin Surface Microscopy)

This non-invasive tool magnifies the skin surface, revealing patterns invisible to the naked eye. For acral lesions, doctors look for:

• Parallel ridge pattern (melanoma pattern)
• Absence of benign patterns like parallel furrow or lattice-like structures
• Irregular blotches and colors

Step 3: Biopsy (The Definitive Test)

A doctor will perform a biopsy by taking a tissue sample from the neoplasm for laboratory analysis. For nail lesions, this may involve removing part of the nail and nail matrix. The pathologist will determine:

• Whether it’s melanoma
• The thickness (Breslow depth) – crucial for staging
• Whether it’s ulcerated
• The mitotic rate (it shows how fast cancer cells are dividing and multiplying)

Step 4: Staging

If melanoma is confirmed, additional tests determine the stage:

• Sentinel lymph node biopsy (for thicker tumors) to check if cancer has spread to nearby lymph nodes
• Imaging (CT, PET, or MRI) for advanced cases to check for distant spread

Acral Lentiginous Melanoma Staging and Prognosis

Staging helps determine treatment and predict outcomes. ALM uses the same staging system (AJCC 8th edition) as other melanomas, but the outcomes are often different.

5-Year Survival Rates by Stage

Why ALM Has a Poorer Prognosis

Studies consistently show that ALM patients have worse outcomes than other melanoma patients, even when diagnosed at the same stage. Several factors contribute:

1. Later diagnosis: ALM is often mistaken for bruises, warts, fungal infections, or calluses, leading to delays
2. Thicker at presentation: ALM tumors are often deeper when first found (median thickness 1.7-2.8mm vs. thinner for sun-related melanomas)
3. Biological differences: ALM has different genetic mutations and a “cold” immune environment that may make it more aggressive
4. Location challenges: The thick skin on palms and soles may allow deeper invasion before detection

Acral Lentiginous Melanoma Treatment

Surgery

For Early Stage (I-II):

• Wide Local Excision (WLE): Removing the tumor with a margin of healthy tissue (typically 1-2 cm margins depending on thickness)
• Sentinel Lymph Node Biopsy: For tumors thicker than 0.8mm, checking the nearest lymph node for microscopic spread

For Advanced Local Disease:

• Amputation: In some cases of subungual melanoma or deeply invasive tumors, partial amputation of a finger or toe may be necessary to ensure complete removal
• Mohs surgery: Specialized technique for precise margin control, though less commonly used for melanoma than for other skin cancers

Adjuvant Therapy (After Surgery)

For high-risk patients (Stage IIB and above, or any node-positive disease), additional treatments reduce recurrence risk:

Immunotherapy:

• Anti-PD1 drugs: Pembrolizumab (Keytruda) or nivolumab (Opdivo) – These “checkpoint inhibitors” help your immune system recognize and attack cancer cells
• Combination therapy: Ipilimumab (Yervoy) + nivolumab for very high-risk cases
• Relatlimab + nivolumab: Newer combination showing promise

Targeted Therapy (for specific genetic mutations):

• BRAF inhibitors: For the rare ALM cases with BRAF V600 mutations (dabrafenib + trametinib)
• KIT inhibitors: For tumors with KIT mutations (imatinib, nilotinib)

Neoadjuvant Therapy (Before Surgery)

An emerging approach where immunotherapy is given before surgery to shrink tumors and reduce spread risk. Studies show that patients who respond well to neoadjuvant therapy have excellent outcomes (89% recurrence-free survival at 2 years for those with complete pathologic response).

Treatment for Metastatic Disease (Stage IV)

When ALM has spread to distant organs:

• Systemic immunotherapy: Combination checkpoint inhibitors are first-line
• Targeted therapy: If specific mutations are present
• Radiation: For symptom control or specific metastases
• Clinical trials: New therapies including LAG-3 inhibitors, TIGIT inhibitors, and combination approaches

If you got diagnosed with ALM: Follow-Up and Survivorship

Surveillance Schedule

After treatment, regular follow-up is crucial because ALM can recur even years later:

• Years 1-3: Every 3-6 months
• Years 4-5: Every 6-12 months
• After 5 years: Annually for life

What to Watch For:

• New lumps or bumps near the surgical site
• Swollen lymph nodes in armpits, groin, or neck
• New spots on palms, soles, or nails
• Unexplained pain, cough, or neurological symptoms

Self-Examination Tips:

• Check your palms, soles, and nails monthly
• Use a hand mirror for hard-to-see areas
• Photograph any moles or spots to track changes
• Don’t ignore “bruises” that don’t heal or dark streaks under nails

Acral Lentiginous Melanoma Specifications Table

Key Takeaways for Patients and Families

1. ALM can affect anyone, regardless of skin color or sun exposure history. This makes it particularly important for people with darker skin to be aware.
2. Check your palms, soles, and nails regularly. Use the CUBED rule to identify suspicious changes.
3. Don’t dismiss “bruises” that don’t fade or “fungal infections” that don’t respond to treatment. These are common misdiagnoses.
4. Hutchinson sign (pigment spreading from nail to skin) is an emergency. See a dermatologist immediately.
5. Early detection saves lives. Stage 0 and I ALM have excellent survival rates (93-100%).
6. ALM requires specialized care. Seek out melanoma specialists and consider academic medical centers familiar with this rare subtype.
7. Treatment is improving. New immunotherapy combinations are showing better results than single-agent therapy.

When to See a Doctor Immediately

Seek urgent dermatological evaluation if you notice:

• A new or changing dark spot on palms, soles, or under nails
• A “bruise” on your foot that hasn’t faded in 2 months
• A dark nail streak that is widening or changing color
• Any pigmentation spreading from under the nail onto the surrounding skin
• A sore on your palm or sole that won’t heal
• Any spot that bleeds, itches, or becomes painful

Sources & References

1. Bradford, PT, Goldstein, AM, McMaster, ML & Tucker, MA 2009, ‘Acral lentiginous melanoma: incidence and survival patterns in the United States, 1986–2005’, Archives of Dermatology, vol. 145, no. 4, pp. 427–434. jamanetwork
2. Holman, DM, Watson, M, Lunsford, NB, Rodriguez, JL & Shoemaker, ML 2023, ‘Acral lentiginous melanoma incidence by sex, race, and ethnicity in the United States’, Journal of the American Academy of Dermatology, published online 24 October 2023. pubmed.ncbi.nlm.nih
3. Fariyike, O et al. 2025, ‘Understanding acral lentiginous melanoma: from the clinic to biology and beyond’, Clinical and Experimental Dermatology, advance online publication 10 November 2025. academic.oup
4. Basurto-Lozada, P et al. 2026, ‘Ancestry and somatic profile indicate acral melanoma as a distinct subtype with variable BRAF activation’, Nature, 17 February 2026. nature
5. ‘Epidemiology, screening and clinical features of acral lentiginous melanoma’ 2025, Journal of Cancer, vol. 16, pp. 3972–3984. jcancer
6. Feci, L, Castriotta, C, De Simone, C & Calvieri, S 2015, ‘Parallel-ridge pattern on dermatoscopy: observation in a case of acral haemorrhage mimicking plantar melanoma’, Anais Brasileiros de Dermatologia, vol. 90, no. 6, pp. 909–912. pmc.ncbi.nlm.nih
7. Lee, SH et al. 2024, ‘Survival rates for invasive cutaneous malignant melanoma in South Korea in accordance with the eighth edition AJCC staging system’, Indian Journal of Dermatology, Venereology and Leprology, vol. 90, no. X, pp. XX–XX. ijdvl
8. Nakamura, Y 2015, ‘Current surgical management of acral lentiginous melanoma’, in Melanoma – Current Clinical Management and Future Therapeutics, IntechOpen, London. intechopen
9. Zheng, Q, Wu, X, Huang, F & Chen, L 2020, ‘Immune checkpoint inhibitors in advanced acral melanoma’, Frontiers in Oncology, vol. 10, article 592844. pmc.ncbi.nlm.nih
10. ‘A comprehensive review and case series of adjuvant and neoadjuvant immunotherapy in acral melanoma’ 2025, Frontiers in Oncology, 13 October 2025. pmc.ncbi.nlm.nih