Quasi‑malignant melanoma (acral lentiginous melanoma) - Symptoms, Causes, Treatment & Prevention

📅 Updated: June 2026 ⏱️ 7 min read ✅ Medically reviewed
```html Quasi‑malignant Melanoma (Acral Lentiginous Melanoma) – A Complete Guide

Quasi‑malignant Melanoma (Acral Lentiginous Melanoma) – A Comprehensive Medical Guide

Overview

Quasi‑malignant melanoma is an older term historically used for what is now called **acral lentiginous melanoma (ALM)**. ALM is a distinct subtype of cutaneous melanoma that arises on the glabrous (non‑hairy) skin of the palms, soles, or under the nails (the nail matrix). Although it behaves like other melanomas, its clinical appearance can resemble benign lesions, which may delay diagnosis.

  • Who it affects: ALM occurs most often in adults over 50, but it can appear at any age. It is the most common melanoma subtype among people of Asian, Black, and Hispanic ancestry, and among Native Americans, where it accounts for up to 70 % of melanomas.[1][2]
  • Prevalence: In the United States, melanoma accounts for about 1 % of all cancer diagnoses (≈ 106,000 new cases in 2024). ALM represents 2–3 % of all cutaneous melanomas overall, but 10–15 % of melanomas in non‑White populations.[3]
  • Prognosis: Because it is often diagnosed at a later stage, ALM has a slightly worse 5‑year survival rate (≈ 65 % for stage III–IV) compared with other melanoma subtypes when matched for stage.[4]

Symptoms

ALM may develop slowly and can mimic benign lesions. Any new, changing, or unusual pigmented area on the palms, soles, or nail unit warrants attention.

  • Asymmetric dark spot – Shape or color that is uneven.
  • Irregular border – Notched, scalloped, or poorly defined edges.
  • Color variation – Shades of brown, black, gray, blue, red, or white within the same lesion.
  • Diameter ≥6 mm – Roughly the size of a pencil eraser, although ALM can be smaller.
  • Evolving lesion – Any change in size, shape, color, or elevation over weeks to months.
  • Peripheral streaking or “satellite” lesions – Small pigmented macules extending from the main lesion.
  • Nail changes (subungual ALM) –
    • Longitudinal brown‑black band (Lentigo) that widens over time.
    • Hutchinson’s sign: pigment extending onto the proximal or lateral nail folds.
    • Ulceration or persistent nail discoloration that does not grow out with the nail.
  • Palmar/plantar ulceration or bleeding – May be misdiagnosed as a wart or chronic ulcer.
  • Itching, tenderness, or pain – Not typical in benign lesions.

Causes and Risk Factors

Biological Mechanisms

ALM originates from melanocytes (pigment‑producing cells) located in the basal layer of acral skin. Unlike other melanomas, UV radiation is *not* the primary driver; instead, genetic mutations (e.g., in **KIT**, **NRAS**, **BRAF**, and **SF3B1**) and chronic mechanical stress appear to play larger roles.[5]

Key Risk Factors

  • Age – Incidence rises after the fifth decade.
  • Skin type – Darker skin tones have a lower overall melanoma risk, but ALM is proportionally higher in these groups.
  • Family history of melanoma – Inherited mutations (e.g., CDKN2A) increase susceptibility.
  • Presence of atypical nevi on acral sites – Rare but noteworthy.
  • Chronic mechanical irritation – Repetitive friction (e.g., from tight shoes, manual labor) may promote malignant transformation.
  • Immunosuppression – Organ‑transplant recipients and patients with HIV have higher melanoma rates.
  • History of other skin cancers – Indicates a field‑defect in DNA repair pathways.

Diagnosis

Early detection relies on a high index of suspicion and systematic evaluation.

Clinical Examination

  • Full‑body skin exam with focus on acral surfaces.
  • Use of the **ABCDE** criteria (Asymmetry, Border, Color, Diameter, Evolution) plus **“F” for “Family/Foot”** when evaluating palms, soles, and nails.

Dermoscopy

A handheld dermatoscope reveals characteristic patterns:

  • Parallel ridge pattern (pigmentation on the ridges of skin lines) – highly specific for melanoma.[6]
  • Irregular parallel furrow pattern – suggests benign lesions.

Biopsy

Definitive diagnosis requires histopathology.

  1. Excisional biopsy with 1–2 mm margins is preferred for lesions ≤ 1 cm.
  2. Punch or incisional biopsy may be used for larger lesions or when the location makes excision difficult.
  3. Pathology assesses Breslow thickness, ulceration, mitotic rate, and presence of lymphovascular invasion.

Staging Tests (once melanoma is confirmed)

  • Sentinel lymph node biopsy (SLNB) – indicated for tumors > 0.8 mm thickness or high‑risk features.
  • Imaging – Ultrasound, CT, PET/CT, or MRI to evaluate regional nodes and distant metastasis based on stage.
  • Blood work – LDH, CBC, liver function tests; used mainly for monitoring advanced disease.

Treatment Options

Treatment follows melanoma guidelines (e.g., NCCN) but is tailored to the acral location.

Surgical Management

  • Wide local excision (WLE) – 1‑cm margin for lesions ≤ 2 mm thickness; 2‑cm margin for > 2 mm, adjusted for anatomic constraints.
  • Amputation or toe‑web excision – Rare, reserved for extensive subungual disease where conservation is impossible.
  • Reconstruction – Skin grafts, local flaps, or dermal substitutes to preserve function of the palm/sole.

Adjuvant Therapy

Recommended for stage II–III disease after surgery.

  • Immune checkpoint inhibitors – Nivolumab or pembrolizumab (PD‑1 blockers) improve recurrence‑free survival.[7]
  • Targeted therapy – For tumors with BRAF V600E/K mutations, combination dabrafenib + trametinib is effective.[8]
  • Interferon‑α – Less commonly used now due to toxicity.

Radiation Therapy

Considered for:

  • Positive margins when further surgery is not feasible.
  • In-transit metastases on the foot/hand.

Systemic Therapy for Advanced Disease

  • PD‑1 monotherapy or combined CTLA‑4 + PD‑1 (e.g., ipilimumab + nivolumab) for stage IV.
  • Targeted agents for BRAF‑mutated tumors.
  • Enroll in clinical trials when possible – many trials focus on acral melanoma, which may respond differently to therapies.[9]

Lifestyle & Supportive Measures

  • Wound care for surgical sites (keep clean, dry, protected).
  • Pain management – NSAIDs, neuropathic agents if nerve involvement.
  • Physical therapy to maintain gait and hand function after extensive surgery.
  • Psychological support – counseling or support groups for melanoma patients.

Living with Quasi‑malignant Melanoma (Acral Lentiginous Melanoma)

Daily Management Tips

  • Self‑examination – Perform a monthly “foot‑and‑hand check” using a mirror or ask a partner to look at hard‑to‑see areas.
  • Footwear – Wear well‑fitting shoes with adequate ventilation; replace worn soles that cause friction.
  • Skin care – Keep acral skin moisturized but avoid heavy ointments that can obscure visual changes.
  • Sun protection – While UV isn’t the main cause, using broad‑spectrum sunscreen on exposed palm/sole surfaces can reduce overall skin cancer risk.
  • Follow‑up schedule – After treatment, dermatology visits every 3–6 months for the first 2 years, then annually.
  • Report new symptoms – Any new lesion, ulceration, or change in a scar should be evaluated promptly.

Emotional & Practical Support

  • Join melanoma survivor networks (e.g., Melanoma Research Foundation).
  • Consider occupational therapy if hand function is impaired.
  • Discuss fertility, pregnancy, or family planning with your oncologist if you are of child‑bearing age – some systemic therapies are contraindicated.

Prevention

  • Routine skin examinations by a dermatologist, especially for individuals with a personal or family history of melanoma.
  • Protect acral skin from chronic trauma – Use padded insoles, change socks daily, break in new shoes gradually.
  • Limit tanning‑bed exposure – Although not a direct cause for ALM, it increases overall melanoma risk.
  • Maintain a healthy immune system – Balanced diet, regular exercise, adequate sleep, and avoidance of smoking.
  • Genetic counseling – For families with multiple melanomas or known high‑risk mutations.
  • Vaccination – HPV vaccine does not affect melanoma but protects against other skin‑related cancers.

Complications

If ALM is not caught early, several serious outcomes may develop:

  • Local invasion – Ulceration, infection, or destruction of underlying structures (tendons, bone).
  • Regional lymph node metastasis – Can cause lymphedema of the leg or arm.
  • Distant metastasis – Common sites: lungs, liver, brain, and bone, leading to organ dysfunction.
  • Secondary infections – Ulcerated lesions can become colonized with bacteria, especially on the foot.
  • Functional loss – Amputation or severe scarring may impair ambulation or hand dexterity.
  • Psychological impact – Depression, anxiety, or body‑image concerns are reported in up to 30 % of melanoma survivors.[10]

When to Seek Emergency Care

Call 911 or go to the nearest emergency department if you notice any of the following:
  • Rapidly enlarging, painful, or bleeding lesion on the hand, foot, or nail.
  • Sudden loss of sensation, severe swelling, or inability to walk/use the affected limb.
  • Fever, chills, or spreading redness suggesting cellulitis around a melanoma ulcer.
  • Signs of systemic illness such as persistent cough, shortness of breath, unexplained weight loss, or neurological changes (confusion, seizures) – possible metastasis.

Prompt medical attention can prevent life‑threatening complications.

References

  1. American Cancer Society. “Melanoma Skin Cancer.” 2024. cancer.org
  2. National Cancer Institute. “Acral Lentiginous Melanoma.” 2023. cancer.gov
  3. CDC. “Cancer Statistics Overview.” 2024. cdc.gov
  4. Balch CM et al. “Final Version of the 2009 AJCC Melanoma Staging System.” *J Clin Oncol*. 2020.
  5. Shain AH, Bastian BC. “The genetics of acral melanoma.” *Nat Rev Clin Oncol*. 2022.
  6. Garbe J et al. “Dermoscopy of acral melanoma: diagnostic features.” *Dermatology*. 2021.
  7. Wang J et al. “Adjuvant pembrolizumab for resected melanoma.” *NEJM*. 2023.
  8. Dummer R et al. “Dabrafenib plus trametinib in BRAF‑mutated melanoma.” *Lancet Oncology*. 2022.
  9. Melanoma Research Foundation. “Clinical Trials for Acral Melanoma.” 2024.
  10. Siegel RL et al. “Psychosocial morbidity in melanoma survivors.” *JAMA Dermatol*. 2021.
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