Acral Lentiginous Melanoma: The Skin Cancer That Hides on Palms, Soles, and Under Nails

You noticed a dark streak running down your nail, or a spot on the sole of your foot that wasn't there before, and a quick search led you here. It's unsettling, especially when the word "melanoma" comes up. Take a breath. Most pigmented spots are harmless, but there is one rare melanoma that hides in exactly these places, and it's worth understanding so you know what to watch for.

Acral lentiginous melanoma (ALM) is a form of skin cancer that develops on the palms, the soles of the feet, and under the fingernails and toenails. It is not caused by the sun, and it affects people of every skin tone. Because it shows up in spots that are easy to overlook, early recognition genuinely matters. Here's what it looks like, how it's diagnosed, and when a spot is worth getting checked.

What is acral lentiginous melanoma?

Acral lentiginous melanoma is a subtype of cutaneous (skin) malignant melanoma that arises on "acral" skin, meaning the hands and feet, and on the nail units. It is the least common form of melanoma overall, accounting for only about 2 to 3 percent of all melanoma diagnoses. But it stands out because, unlike most melanomas, ultraviolet (sun) exposure is not a primary cause. ALM develops on palms, soles, fingers, toes, and beneath nails, areas that get little to no sun.

ALM also has a distinct biology. Research published by the American Academy of Dermatology describes it as molecularly different from sun-driven melanomas, with low overall mutation rates and more large-scale chromosomal changes. That difference is part of why it doesn't respond to UV the way other melanomas do.

Who gets it, and why it matters for darker skin tones

ALM occurs in people of all skin colors at roughly equal rates. But because sun-driven melanomas are far less common in people with more melanin, ALM makes up a much larger share of melanoma cases in non-White populations. It represents an estimated 40 to 60 percent of melanoma diagnoses in Asian and African-American populations, and is the most common melanoma type diagnosed in people with darker skin.

The average age at diagnosis is around 63, and incidence rises with age. In U.S. cancer registry data, ALM made up the largest proportion of melanoma subtypes among Black patients (roughly a third of their melanoma cases). This is why the long-held "melanoma only happens to fair, sunburned skin" message is misleading, and why checking palms, soles, and nails matters for everyone.

What does acral lentiginous melanoma look like?

ALM can be easy to mistake for something harmless, like a bruise, a callus, a wart, a blood blister, or a fungal nail infection. That's a big reason it is often caught late. The dermatologist's "ABCDE" rule for melanoma is a useful starting point, with a few acral-specific signs to add.

Watch for these warning features on the hands, feet, and nails:

• A new or changing dark spot on a palm or sole that is asymmetric, has irregular or blurry borders, has more than one color, or is larger than about 6 mm (a pencil eraser)
• A pigmented area that keeps growing or changing over weeks to months
• A dark band or stripe running lengthwise down a nail, especially if it is widening, getting darker, or appears on a single nail
• Hutchinson sign: pigment that spreads from the nail onto the surrounding skin or nail fold (a worrying feature, though not 100 percent specific)
• A nail change such as splitting, cracking, ulceration, or bleeding that doesn't heal
• A foot or hand sore or "blood blister" that won't go away

How is it diagnosed?

Diagnosis starts with a clinician examining the spot, often with a dermatoscope (a handheld magnifier with light). The only way to confirm melanoma is a skin biopsy, where a small sample of tissue is removed and examined under a microscope. For nail-unit (subungual) melanoma, the biopsy needs to be taken from the nail matrix, the tissue at the base of the nail where pigment is produced, which is why this is done by a specialist.

Once melanoma is confirmed, the most important measurement is the Breslow thickness, or how deep the tumor extends into the skin. Thickness, along with cancer staging and whether the nearest (sentinel) lymph node is involved, drives both treatment and prognosis. Unfortunately, ALM is frequently diagnosed at an advanced stage: in one analysis the mean Breslow thickness at diagnosis was 4.8 mm, with the majority of cases already deep into the skin. Subungual ALM most often involves the thumb or great toe, which together account for about 92 percent of nail-unit cases.

Survival and why early detection is so important

ALM tends to have a poorer prognosis than other melanomas, largely because it is caught later, not because of where it sits on the body. In U.S. registry data, five-year melanoma-specific survival for ALM was about 80 percent, compared with roughly 91 to 93 percent for cutaneous melanoma overall. Survival also varies across groups, and has been reported as lower in Hispanic White patients than in Non-Hispanic White or Black patients, a gap thought to reflect later-stage diagnosis and access to care.

The encouraging flip side: outcomes depend heavily on how early ALM is found. A thin, early melanoma that is removed promptly has a much better outlook than a thick, advanced one. That is the whole case for knowing the signs and not dismissing a changing spot on your hands, feet, or nails.

When to see a doctor

See a dermatologist promptly if you notice a new or changing dark spot on a palm or sole, a new pigmented stripe in a single nail, pigment spreading onto the skin around a nail, or a sore on the hand or foot that won't heal. None of these guarantees cancer, and many turn out to be benign, but they are worth a professional look because early ALM is so treatable.

Don't wait for a spot to become painful; melanoma is often painless. If you have darker skin, this matters just as much for you, possibly more, since ALM is the most common melanoma type in darker skin tones and is often diagnosed late. A clinician can examine the area, perform dermoscopy, and biopsy anything suspicious. When in doubt, get it checked. This article is general education, not a diagnosis, so an in-person evaluation is always the right next step for a worrying spot.