Acral melanoma is a form of skin cancer that develops on the hairless skin of the palms, soles of the feet, and under or around the nails. Unlike the more familiar types of melanoma that tend to appear on sun-exposed areas of the body, acral melanoma arises in places most people never think to check for cancer. It accounts for a small fraction of all melanomas in light-skinned populations but represents a far larger share of melanomas diagnosed in people with darker skin, and it carries a reputation for being caught late because both patients and clinicians frequently mistake it for something harmless.
Where Acral Melanoma Develops and Who It Affects
Acral melanoma grows specifically on “glabrous” skin, which is the thick, ridged skin found on the palms of the hands, the soles of the feet, and in the nail unit (the nail bed plus the surrounding folds of skin).1PubMed Central. Acral lentiginous melanoma: Basic facts, biological characteristics and research perspectives of an understudied disease The sole of the foot is the single most common location, and within the sole, the weight-bearing zones at the heel and ball of the foot are disproportionately affected.2Scientific Reports. A clinicopathological analysis of 153 acral melanomas and the relevance of mechanical stress
A common misconception is that acral melanoma is a “disease of dark skin.” In absolute numbers, non-Hispanic White individuals actually have the highest incidence, at roughly 2.3 cases per million. Hispanic White individuals have an even higher rate, at about 2.8 per million.3PubMed Central. Acral lentiginous melanoma incidence by sex, race, ethnicity, and stage in the United States, 2010–2019 Where the racial disparity becomes stark is in the proportion of melanomas that turn out to be acral. Among non-Hispanic White people, fewer than 1% of all melanomas are acral. Among Hispanic Black, American Indian/Alaska Native, and Asian/Pacific Islander populations, that figure jumps to about 19%.3PubMed Central. Acral lentiginous melanoma incidence by sex, race, ethnicity, and stage in the United States, 2010–2019 So while other types of melanoma are far less common in people of color, acral melanoma is not, and it can easily become the dominant form of melanoma in those populations.
The overall incidence of acral melanoma has been climbing. From 2000 to 2020, the age-adjusted incidence rose by about 2.5% annually in the United States, driven mainly by increases among Hispanic and non-Hispanic White individuals.4PubMed. Trends by race and ethnicity in incidence and mortality of acral lentiginous melanoma: analysis of Surveillance, Epidemiology, and End Results 2000-2020 At the same time, mortality from acral melanoma is significantly worse for racial and ethnic minorities. Compared to non-Hispanic White patients, the risk of dying from acral melanoma is roughly 40% higher in Hispanic patients, 60% higher in Asian/Pacific Islander patients, and more than double in non-Hispanic Black patients, even after adjusting for other factors.4PubMed. Trends by race and ethnicity in incidence and mortality of acral lentiginous melanoma: analysis of Surveillance, Epidemiology, and End Results 2000-2020 Delayed diagnosis is widely thought to be a major contributor to that gap.
What Causes Acral Melanoma
This is one of the genuinely puzzling aspects of the disease. The palms and soles receive comparatively little ultraviolet radiation, so the standard explanation for melanoma (accumulated sun damage to skin cells) does not map cleanly onto acral melanoma. Researchers have increasingly focused on mechanical stress as a potential driver. In a study of 313 acral melanoma patients in Korea, about 27% reported a traumatic event and 29% reported chronic physical stress at the site before the melanoma appeared. Farmers and fishermen, occupations involving heavy use of hands and feet, made up the largest occupational group in that cohort.5PubMed Central. Frequency of Trauma, Physical Stress, and Occupation in Acral Melanoma: Analysis of 313 Acral Melanoma Patients in Korea
The pattern also shows up anatomically. An analysis of 153 plantar melanomas found that stress-bearing areas of the sole, specifically the heel and the ball of the foot, were significantly more likely to harbor melanoma than non-weight-bearing zones like the arch.2Scientific Reports. A clinicopathological analysis of 153 acral melanomas and the relevance of mechanical stress That distribution held regardless of age, sex, tumor thickness, or stage, which makes it difficult to write off as coincidence. One proposed mechanism is that repeated mechanical force destabilizes the nuclear membranes of skin cells at those sites, creating genomic errors that set the stage for cancer.6PubMed. Mechanical Stress as a Pathomechanism of Plantar Acral Melanoma
Laboratory work has added detail to this picture. Melanocytes, the pigment-producing cells where melanoma originates, turn out to be sensitive to the physical properties of their environment. Research has shown that the proteins making up the tissue scaffold surrounding melanocytes can switch those cells between a settled, pigment-producing state and a more mobile, less differentiated state. The signaling pathway involved runs through a chain of molecular switches that respond to mechanical cues from the surrounding tissue.7PubMed Central. Melanocyte differentiation and mechanosensation are differentially modulated by distinct extracellular matrix proteins This does not prove that walking causes acral melanoma, but it does suggest that the cells most susceptible to this cancer are wired to respond to physical force in ways that could tip them toward malignancy.
The Genetic Profile Is Different from Other Melanomas
Acral melanoma is not just melanoma in an unusual location. Its underlying genetic fingerprint is distinct. Sun-related melanomas typically carry mutations in the BRAF gene, which is the target of drugs like vemurafenib. Acral melanomas have a much lower rate of BRAF mutations and instead tend to accumulate large-scale structural rearrangements in their DNA rather than the individual point mutations more common in UV-driven tumors.
A detailed genomic study found that about 80% of acral melanomas harbor “hailstorm” patterns of chaotic gene amplification, frequently involving chromosomes that carry cancer-relevant genes like TERT, CCND1, CDK4, and MDM2. The TERT gene, which helps cancer cells achieve unlimited growth, was altered in roughly 70% of cases.8Nature Communications. The genetic evolution of acral melanoma Ancestry also shapes the genetic profile. East Asian patients with acral melanoma tend to have fewer point mutations and structural variations overall, with a higher rate of NRAS mutations and a lower rate of BRAF mutations compared to patients of European descent.9PubMed. Genomic characterization reveals distinct mutational landscape of acral melanoma in East Asian These differences matter clinically because they influence which targeted therapies are likely to work.
How to Recognize the Symptoms
Acral melanoma’s appearance depends on where it grows. On the palms and soles, it typically starts as a dark or multicolored flat patch that expands slowly. The borders are often irregular, and the color can range from brown or black to areas with no pigment at all. Some acral melanomas are entirely amelanotic (lacking visible pigment), which makes them especially easy to overlook.
Under the nail, acral melanoma usually presents as a dark longitudinal streak running from the cuticle to the tip of the nail. One of the hallmark warning signs is the Hutchinson sign, which refers to pigment spreading from beneath the nail into the surrounding skin folds. This sign appeared from the early stages of disease in almost all cases in a histological review of 50 subungual melanomas.10PubMed. Subungual melanoma: histological examination of 50 cases from early stage to bone invasion The extent of the Hutchinson sign correlates with how advanced the tumor is: when pigmentation involves three or more nail folds, the tumor tends to be at a significantly higher stage.11PubMed. Clinical features of subungual melanoma according to the extent of Hutchinson’s nail sign: a retrospective single-centre study
It is worth knowing, though, that the Hutchinson sign is not absolute proof of melanoma. A “pseudo-Hutchinson sign” can occur when dark pigment simply shows through a translucent cuticle without any cancer being present. Experts still strongly recommend biopsy whenever the sign is observed, given its close association with subungual melanoma, but clinicians should be aware that it is not exclusive to melanoma, particularly in children.12Actas Dermo-Sifiliográficas. Is Hutchinson’s Sign Pathognomic of Subungual Melanoma?
Why It Gets Misdiagnosed So Often
Acral melanoma has earned the label “the great pretender” in dermatology literature, and the data backs that up. At one major U.S. academic center, roughly a third of acral melanoma cases were initially given the wrong diagnosis. The list of misdiagnoses is striking: warts, calluses, fungal infections, foreign bodies, blisters, nonhealing wounds, ingrown toenails, and subungual hematomas (the “bruise under the nail” you might get from stubbing a toe).13PubMed. Acral lentiginous melanoma mimicking benign disease: the Emory experience In at least one documented case, a hyperkeratotic (thick, scaly) acral melanoma was treated as a common wart for long enough that the patient eventually required thumb amputation.14PubMed Central. Hyperkeratotic acral melanoma mimicking a common wart
Several factors conspire to create diagnostic delays. Many people do not regularly inspect the soles of their feet. Clinicians may not associate melanoma with non-sun-exposed areas, especially in patients with darker skin. And acral melanoma can mimic vascular lesions and infections, adding to the confusion.15PubMed. Melanoma of the feet: misdiagnosed and misunderstood Any pigmented lesion on the palm, sole, or under a nail that is changing in size, shape, or color, or any nonhealing wound in those areas, should prompt a visit to a dermatologist.
How Dermoscopy Helps
Dermoscopy, which uses a handheld magnifying device with polarized light, is a critical tool for evaluating suspicious acral lesions. On the ridged skin of the palms and soles, one dermoscopic pattern stands out as a strong melanoma indicator: the parallel ridge pattern, where pigment follows the ridges of the skin’s surface rather than the grooves (sulci). This pattern carries roughly 99% specificity for melanoma according to the literature, meaning that when it appears, it almost never turns out to be benign.16PubMed Central. Parallel ridge pattern on dermoscopy: observation in non-melanoma cases That said, the parallel ridge pattern is not always present in acral melanoma, and rare benign conditions can mimic it, so dermoscopy supplements clinical judgment rather than replacing it.
What Determines Prognosis
The two strongest predictors of survival in acral melanoma are tumor thickness and disease stage at the time of diagnosis. A large study found that tumors thicker than 2 mm and more advanced stage at presentation were both significantly associated with worse melanoma-specific survival. Race and ethnicity, when adjusted for tumor characteristics and treatment, were not independently associated with survival.17British Journal of Dermatology. Prognostic factors and survival in acral lentiginous melanoma That finding underscores the role of diagnostic delay in driving the worse mortality seen in minority populations: the cancer itself is not inherently more aggressive in any racial group, but it is caught later more often in communities where both patients and doctors are less likely to suspect melanoma on acral sites.
Ulceration, where the surface skin over the tumor breaks down, also affects outcomes, but its impact is uneven. In thin acral melanomas (1 mm or less), ulceration is a powerful danger sign, associated with roughly eight times the risk of melanoma-specific death compared to non-ulcerated thin tumors.18British Journal of Dermatology. Prognostic value of ulceration varies across Breslow thicknesses and clinical stages in acral melanoma In thicker tumors, though, the survival difference between ulcerated and non-ulcerated melanomas was not statistically significant, suggesting that other factors dominate prognosis once the tumor has already grown deep.
Surgical Treatment and the Shift Away from Amputation
Surgery is the primary treatment for localized acral melanoma. For tumors on the palms and soles, this means wide excision with margins that match the tumor’s thickness, following the same staging guidelines used for melanoma elsewhere on the body. Reconstruction of the sole of the foot after excision can be challenging. The thick plantar skin is not very mobile, so primary wound closure is often impossible. Skin grafts have been used but tend to darken heavily during healing, which creates both cosmetic problems and practical difficulties in monitoring the site for recurrence. Flap techniques generally offer better long-term results but require longer healing times.19PubMed Central. Acral melanoma: considerations about the surgical management of this tumor
For melanoma under the nail, amputation of the affected finger or toe was long considered the gold standard. That assumption, however, was never based on strong comparative evidence.20PubMed Central. Salvaging the Digit in Invasive Subungual Malignancies Using a Triple Technique under Awake Local Anesthesia Over the past decade, digit-sparing surgery has gained traction, especially for melanoma in situ (confined to the surface layer of skin). Techniques that remove the entire nail bed unit and shave the underlying bone, followed by flap coverage, have shown no local or distant recurrence in early follow-up for select patients with invasive disease.20PubMed Central. Salvaging the Digit in Invasive Subungual Malignancies Using a Triple Technique under Awake Local Anesthesia The conversation between surgeon and patient now increasingly weighs functional preservation against oncologic safety, rather than defaulting to amputation.21PubMed. Function-sparing surgery for subungual melanoma in situ
Immunotherapy and Targeted Drugs for Advanced Disease
When acral melanoma has spread beyond the original site, systemic therapy becomes necessary. Immune checkpoint inhibitors, the same class of drugs that revolutionized treatment for sun-related melanoma, do work in acral melanoma, but response rates tend to be lower. A study comparing treatment approaches found that the combination of anti-PD-1 and ipilimumab produced a response in about 43% of acral melanoma patients, compared to 26% with anti-PD-1 alone and 15% with ipilimumab alone.22Journal for ImmunoTherapy of Cancer. Efficacy of anti-PD-1 and ipilimumab alone or in combination in acral melanoma Despite the higher response rate with the combination, it did not translate into a statistically significant improvement in overall survival compared to anti-PD-1 alone, possibly because many patients received additional therapies after their initial treatment and because resistance to immunotherapy developed frequently.
Targeted therapy is a different story in acral melanoma than in other melanoma subtypes. Because BRAF mutations are less common, the BRAF inhibitors that are mainstays in other melanomas are relevant for only a subset of acral patients. Acral melanomas more frequently harbor KIT mutations or amplifications, and the drug imatinib (originally developed for leukemia) has been tested against these tumors. In a trial of patients with KIT-altered melanomas arising on acral, mucosal, or chronically sun-damaged skin, the overall response rate was about 29%. But the response depended entirely on the type of KIT change: patients with true KIT mutations responded at a rate of 54%, while those with KIT amplification alone had a 0% response rate.23PubMed Central. Imatinib for Melanomas Harboring Mutationally Activated or Amplified KIT Arising on Mucosal, Acral, and Chronically Sun-Damaged Skin That sharp divide illustrates why molecular profiling of the tumor matters so much for treatment planning.
Research into combination strategies is ongoing. CDK4/6 inhibitors, anti-angiogenic drugs, and agents like albumin-bound paclitaxel are being explored as partners for immune checkpoint inhibitors, with the rationale that combining approaches could overcome the resistance that often develops with immunotherapy alone.24PubMed Central. Advanced Acral Melanoma Therapies: Current Status and Future Directions
Artificial Intelligence in Acral Melanoma Diagnosis
Because acral melanoma is relatively rare and easy to confuse with benign conditions, it is a natural testing ground for AI-assisted diagnosis. Several research groups have trained convolutional neural networks (a type of deep learning model) on dermoscopic images of acral lesions and compared the AI’s performance to that of human clinicians.
In one study, a neural network matched expert dermatologists in diagnostic accuracy for acral melanoma, scoring around 83% compared to the experts’ 81%, while non-expert clinicians managed only about 68%.25PLOS ONE. Acral melanoma detection using a convolutional neural network for dermoscopy images Another group achieved close to 97% accuracy using transfer learning techniques.26PubMed Central. Acral melanoma detection using dermoscopic images and convolutional neural networks Perhaps the most practical finding came from a study that tested “augmented decision-making,” where clinicians made their diagnosis first and then were shown the AI’s assessment. When clinicians had AI support, their accuracy rose from about 75% to 87%, and agreement among different clinicians also improved substantially.27PubMed. Augmented decision-making for acral lentiginous melanoma detection using deep convolutional neural networks
None of these tools are in routine clinical use yet, and they perform best on the kind of clean dermoscopic images they were trained on, which is not always what a busy clinic produces. But for a cancer whose main obstacle is delayed recognition, AI that helps less-experienced clinicians approach expert-level accuracy has obvious potential, particularly in settings without ready access to a dermatologist specializing in pigmented lesions.
Why Definitions Still Create Problems
One underappreciated wrinkle in acral melanoma research is that experts do not always agree on what counts as “acral melanoma.” Some define it by anatomic location: any melanoma on the palms, soles, or nail apparatus. Others define it by histological subtype, specifically the acral lentiginous pattern, which is a particular way the tumor cells spread along the base of the epidermis. These two definitions overlap but are not identical. A melanoma on the sole can have a non-lentiginous growth pattern, and a lentiginous growth pattern can occasionally appear outside the classic acral sites. This inconsistency complicates everything from clinical trials to survival statistics, because studies that define the disease differently end up studying somewhat different patient populations.28medRxiv. Revisiting the Definition of Acral Melanoma: Unraveling Histology and Location For patients, the practical takeaway is that when you read statistics about acral melanoma, the numbers may shift depending on how the researchers drew the boundaries of the disease.