Acral melanoma is a specific subtype of skin cancer that originates from pigment-producing cells called melanocytes. It characteristically develops on the palms of the hands, the soles of the feet, or beneath the nails. Unlike more common melanomas, this type is not strongly associated with sun exposure, and its inconspicuous nature can lead to diagnosis at a more advanced stage.
Identifying Acral Melanoma
The physical signs of acral melanoma can be subtle, making self-examination of hands and feet important for early detection. On the palms and soles, the cancer often appears as a dark spot, patch, or streak that may be black or dark brown. These spots can also be lightly colored with shades of red, tan, or pink, and some are colorless, which can delay recognition. The borders of these lesions are frequently irregular, and the shape or color may change over time.
A “parallel ridge pattern” is a telling sign, visible with a magnifying tool called a dermoscope. This pattern, where pigmentation follows the skin’s ridges on the palms or soles, indicates melanoma. In contrast, benign spots (nevi) on these areas show pigmentation in the furrows, the finer lines between the main ridges.
When acral melanoma develops under a fingernail or toenail, it is called subungual melanoma. It often presents as a dark, longitudinal band, brown or black, that stretches from the nail base to its edge. This feature is known as Hutchinson’s sign, especially when the pigment extends to the surrounding skin of the nail fold. The band may widen over time, particularly at its base near the cuticle.
The “ABCDE” guide for identifying melanomas (Asymmetry, Border, Color, Diameter, Evolving) is adapted for acral melanoma. While asymmetry and irregular borders are still relevant, the focus shifts to any new or changing spot on the hands or feet. For subungual melanoma, any new band of color, especially one that is wider than 3 millimeters, changes, or damages the nail plate, warrants medical evaluation.
Risk Factors and Causes
The causes of acral melanoma are not fully understood, but evidence suggests a different biological pathway than other skin cancers. The cancer originates from melanocytes on the palms and soles, which may explain its distinct characteristics.
This type of melanoma is the most common form diagnosed in people with darker skin tones, including individuals of African, Asian, and Hispanic descent. While the overall incidence of melanoma is lower in these populations, acral melanoma constitutes a much larger proportion of their cases.
While the exact cause remains unknown, genetic factors are thought to play a role. Certain genetic mutations, such as in the KIT proto-oncogene, are more frequently associated with acral melanoma. Some research has also explored whether physical trauma or pressure to the palms or soles could be a contributing factor, though a definitive link has not been established.
Diagnosis and Staging
Any suspicious spot or streak on the palms, soles, or under the nails should be evaluated by a dermatologist. An early and accurate diagnosis is foundational to effective treatment. The diagnostic process begins with a clinical examination, where a doctor inspects the lesion, paying close attention to its size, shape, color, and any recent changes.
A dermatologist will use a dermoscope to get a clearer view of the structures beneath the skin’s surface. This examination helps identify suspicious patterns not visible to the naked eye. If the dermoscopic examination raises suspicion, the next step is a biopsy, which involves the surgical removal of the suspicious tissue for microscopic analysis by a pathologist.
If a biopsy confirms a diagnosis of acral melanoma, the next step is staging. Staging is a system used to determine the extent of the cancer, which helps guide treatment decisions. The pathologist will assess features like the tumor’s thickness (Breslow depth) and whether the skin over the lesion is broken (ulceration). Further tests may be performed to see if the cancer has spread to nearby lymph nodes or other parts of the body.
Treatment Approaches
Surgical excision is the main treatment for acral melanoma that is confined to its original location. The goal of the surgery is to remove the entire cancerous tumor along with a surrounding margin of healthy tissue. The width of this safety margin depends on the thickness of the tumor. In some cases, particularly on a finger or toe, this may require a skin graft or even partial amputation to ensure all cancerous cells are removed.
For melanomas that have grown deeper or spread to other parts of the body, additional treatments are necessary. These advanced therapies are designed to target cancer cells throughout the body. The specific approach depends on the cancer’s stage and molecular characteristics. Combining therapies is a common strategy to address more advanced disease.
Immunotherapy is a treatment that uses the body’s own immune system to fight cancer, and drugs known as immune checkpoint inhibitors have become a standard option. Targeted therapy involves medications that focus on specific genetic mutations within the cancer cells, such as the KIT mutations sometimes found in acral melanoma. Radiation therapy or chemotherapy may also be considered in certain situations to control the disease.