Acral lentiginous melanoma (ALM) is a type of skin cancer that develops on the palms of the hands, soles of the feet, or under the fingernails and toenails. Unlike the more common forms of melanoma linked to sun exposure, ALM grows on areas that rarely see sunlight, which means it often goes unnoticed until it has progressed. It accounts for a small fraction of all melanoma cases overall, but it is the most common subtype in people with darker skin tones.
Where ALM Develops and What It Looks Like
ALM appears in “acral” areas, meaning the extremities: the soles of the feet, the palms, and the nail bed. On the skin, it typically starts as a flat, irregularly shaped patch of dark pigmentation that spreads outward slowly before growing deeper into the tissue. The borders are often uneven, and the color can range from brown to black, sometimes with areas of lighter pigmentation mixed in. On the soles or palms, it can resemble a bruise or stain that doesn’t fade over time.
When ALM develops under a nail, it usually appears as a dark streak running lengthwise down the nail. One important warning sign is the Hutchinson sign, where the dark pigmentation extends beyond the nail itself onto the surrounding skin of the cuticle or fingertip. This spread of color beyond the nail borders is a red flag that warrants immediate evaluation. Not every dark nail streak is melanoma, but any new or changing streak, especially one that is wider than 3 millimeters or involves a single nail, should be examined.
Part of what makes ALM dangerous is how easily it mimics other conditions. It can look like a plantar wart, a fungal infection, a diabetic ulcer, or simple trauma to the nail. These misidentifications contribute to later-stage diagnoses. Generally, any pigmented lesion on acral skin larger than 7 millimeters should be biopsied.
Who Gets ALM
ALM is rare in the broader population, but its distribution across racial and ethnic groups is strikingly uneven. Among non-Hispanic White individuals, ALM represents only about 0.8% of all melanoma diagnoses. Among Hispanic, Black, American Indian/Alaska Native, and Asian/Pacific Islander populations, that figure jumps to roughly 19%. This doesn’t mean ALM is more common in these groups in absolute numbers. It means that when melanoma does occur in people with darker skin, it is disproportionately likely to be this specific subtype.
Because melanoma awareness campaigns have historically focused on sun-related risk factors and fair skin, ALM in darker-skinned individuals is frequently diagnosed later. The locations where it grows, particularly the soles of the feet, are areas people rarely examine closely. Bob Marley’s death from melanoma that began under his toenail remains one of the most widely known examples of how this cancer can be overlooked.
How ALM Differs From Other Melanomas
Most melanomas carry a genetic mutation called BRAF, which has become a key target for treatment. ALM has a different molecular profile. In ALM, BRAF mutations appear in only about 16% of cases, compared to roughly 50% in sun-related melanomas. NRAS mutations occur in about 14.5% of cases, and KIT mutations in about 11.8%. This distinct genetic makeup has real consequences for treatment, since the targeted therapies designed for BRAF-mutated melanomas are not effective for the majority of ALM patients.
ALM also behaves differently in terms of growth pattern. It tends to spend a longer period in a “radial” growth phase, spreading outward across the skin surface before invading deeper layers. This longer horizontal phase theoretically offers a window for early detection, but because the locations are hard to see and the appearance is easily mistaken for something benign, that window is frequently missed.
Diagnosis and Staging
Diagnosing ALM requires a biopsy. For lesions on the skin of the palm or sole, a punch biopsy or excisional biopsy captures a sample of tissue for examination under a microscope. For suspected nail melanoma, the process is more involved, sometimes requiring a nail matrix biopsy where the nail is partially or fully removed to access the tissue underneath. In some cases, multiple biopsy sites are needed to determine whether the melanoma has remained in the outermost layer of skin (in situ) or has begun to invade deeper.
Once diagnosed, the most important measurement is Breslow thickness, which is the depth of the melanoma in millimeters. Thinner tumors have significantly better outcomes. A large study of 853 patients with acral melanoma found that survival dropped meaningfully as tumors progressed from thin (T1) to moderate (T2 and T3) thickness. Interestingly, once tumors exceeded 2 millimeters in thickness, survival outcomes were similar regardless of how much thicker they grew. This suggests that the critical window is catching the cancer before it reaches that 2-millimeter threshold.
Treatment Approaches
Surgery is the primary treatment for ALM that has not spread beyond its original site. The goal is to remove the melanoma along with a margin of healthy tissue around it. On the sole of the foot or palm, this is a standard wide excision, though the location can make wound closure and healing more complicated than on other body parts. For nail melanomas, treatment may involve removing the nail and the underlying nail bed. In some cases, particularly when the tumor is thick or involves the bone, partial amputation of a finger or toe is necessary.
For advanced ALM that has spread to lymph nodes or distant organs, immunotherapy is the main systemic treatment. These drugs work by helping the immune system recognize and attack cancer cells. A large registry study compared outcomes for ALM patients receiving immunotherapy to those with other types of cutaneous melanoma. The overall best response rates were similar between the two groups, which is encouraging given earlier concerns that ALM might be less responsive. However, overall survival numbers for ALM patients receiving combination immunotherapy were lower (17.8 months) compared to those on single-agent immunotherapy (26 months), though this difference was not statistically significant and may reflect differences in disease severity among patients who received more aggressive treatment.
Because ALM less commonly carries the BRAF mutation, fewer patients are candidates for targeted therapy drugs that block that specific pathway. For the subset who do have targetable mutations, including KIT mutations, clinical trials and targeted agents may offer additional options.
Survival and Prognosis
When caught early, ALM is highly treatable. Five-year overall survival for stage I ALM is 84.6%, compared to 88.6% for other cutaneous melanomas at the same stage. At stage II, the gap narrows further: 62.1% for ALM versus 64%. The difference becomes more pronounced at stage III, where ALM survival is 47.5% compared to 56.7% for other melanomas. By stage IV, outcomes converge again at roughly 16% for both types.
The slightly worse outcomes at early and middle stages likely reflect a combination of factors: ALM tends to be diagnosed at greater thickness, the acral locations make achieving clear surgical margins more challenging, and the biology of the tumor may be inherently more aggressive in some cases. The pattern reinforces how much early detection matters. The survival difference between stage I and stage III is dramatic, and most of that gap comes down to when the cancer was found.
What to Look For
Checking your palms, soles, and nails periodically can catch ALM at its most treatable stage. On the skin, watch for any new dark spot or patch that grows, changes shape, or has irregular borders. On the nails, a new dark streak that widens over time, involves only one nail, or causes pigmentation to bleed into the surrounding skin deserves attention. Any non-healing sore on the sole of the foot or palm that persists for weeks without explanation should also be evaluated.
People with darker skin tones should be especially aware, since ALM represents a disproportionate share of melanoma diagnoses in these populations and is more likely to be missed or misdiagnosed. A dermatologist familiar with pigmented lesions on acral skin can use dermoscopy, a magnified examination technique, to distinguish suspicious lesions from benign ones like ethnic nail pigmentation or simple moles.